diff --git a/fsw/cfe-core/src/es/cfe_es_api.c b/fsw/cfe-core/src/es/cfe_es_api.c
index 916264a1d..f22a9e366 100644
--- a/fsw/cfe-core/src/es/cfe_es_api.c
+++ b/fsw/cfe-core/src/es/cfe_es_api.c
@@ -1602,6 +1602,11 @@ int32 CFE_ES_WriteToSysLog(const char *SpecStringPtr, ...)
     int32         ReturnCode;
     va_list       ArgPtr;
 
+    if (SpecStringPtr == NULL)
+    {
+        return CFE_ES_BAD_ARGUMENT;
+    }
+
     va_start(ArgPtr, SpecStringPtr);
     CFE_ES_SysLog_vsnprintf(TmpString, sizeof(TmpString), SpecStringPtr, ArgPtr);
     va_end(ArgPtr);
@@ -1633,6 +1638,11 @@ uint32 CFE_ES_CalculateCRC(const void *DataPtr, size_t DataLength, uint32 InputC
     const uint8 *BufPtr;
     uint8  ByteValue;
 
+    if (DataPtr == NULL || DataLength == 0)
+    {
+        return InputCRC;
+    }
+
     static const uint16 CrcTable[256]=
     {
 
@@ -1727,46 +1737,60 @@ int32 CFE_ES_RegisterCDS(CFE_ES_CDSHandle_t *CDSHandlePtr, size_t BlockSize, con
     /* Check to make sure calling application is legit */
     Status = CFE_ES_GetAppID(&ThisAppId);
 
-    if ( Status != CFE_SUCCESS )  /* Application ID was invalid */
-    {
-         CFE_ES_WriteToSysLog("CFE_CDS:Register-Bad AppId context\n");
-    }
-    else if (!CFE_ES_Global.CDSIsAvailable)
+    if ( Status != CFE_SUCCESS || CDSHandlePtr == NULL || Name == NULL)  /* Application ID was invalid */
     {
-        CFE_ES_WriteToSysLog("CFE_CDS:Register-CDS not available\n");
-        Status = CFE_ES_NOT_IMPLEMENTED;
+      CFE_ES_WriteToSysLog("CFE_ES_RegisterCDS:-Failed invalid arguments\n");
+      Status = CFE_ES_BAD_ARGUMENT;
     }
     else
     {
-        /* Assume we can't make a CDS and return a bad handle for now */
-        *CDSHandlePtr = CFE_ES_CDS_BAD_HANDLE;
-
-        /* Make sure specified CDS name is not too long or too short */
-        NameLen = strlen(Name);
-        if ((NameLen > CFE_MISSION_ES_CDS_MAX_NAME_LENGTH) || (NameLen == 0))
-        {
-           Status = CFE_ES_CDS_INVALID_NAME;
+        /* Initialize output to safe value, in case this fails */
+        *CDSHandlePtr = CFE_ES_RESOURCEID_UNDEFINED;
 
-           /* Perform a buffer overrun safe copy of name for debug log message */
+        /* Check to make sure calling application is legit */
+        Status = CFE_ES_GetAppID(&ThisAppId);
 
-           strncpy(CDSName, Name, sizeof(CDSName) - 1);
-           CDSName[sizeof(CDSName) - 1] = '\0';
-           CFE_ES_WriteToSysLog("CFE_CDS:Register-CDS Name (%s) is too long\n", CDSName);
+        if ( Status != CFE_SUCCESS )  /* Application ID was invalid */
+        {
+            CFE_ES_WriteToSysLog("CFE_CDS:Register-Bad AppId context\n");
+        }
+        else if (!CFE_ES_Global.CDSIsAvailable)
+        {
+            CFE_ES_WriteToSysLog("CFE_CDS:Register-CDS not available\n");
+            Status = CFE_ES_NOT_IMPLEMENTED;
         }
         else
         {
-           /* Modify specified name to be processor specific name */
-           /* of the form "AppName.Name"                          */
-           CFE_ES_FormCDSName(CDSName, Name, ThisAppId);
+            /* Assume we can't make a CDS and return a bad handle for now */
+            *CDSHandlePtr = CFE_ES_CDS_BAD_HANDLE;
 
-           /* Create CDS and designate it as NOT being a Critical Table */
-           Status = CFE_ES_RegisterCDSEx(CDSHandlePtr, BlockSize, CDSName, false);
+            /* Make sure specified CDS name is not too long or too short */
+            NameLen = strlen(Name);
+            if ((NameLen > CFE_MISSION_ES_CDS_MAX_NAME_LENGTH) || (NameLen == 0))
+            {
+                Status = CFE_ES_CDS_INVALID_NAME;
 
-           /* If size is unacceptable, log it */
-           if (Status == CFE_ES_CDS_INVALID_SIZE)
-           {
-              CFE_ES_WriteToSysLog("CFE_CDS:Register-CDS %s has invalid size (%lu)\n", Name, (unsigned long)BlockSize);
-           }
+                /* Perform a buffer overrun safe copy of name for debug log message */
+
+                strncpy(CDSName, Name, sizeof(CDSName) - 1);
+                CDSName[sizeof(CDSName) - 1] = '\0';
+                CFE_ES_WriteToSysLog("CFE_CDS:Register-CDS Name (%s) is too long\n", CDSName);
+            }
+            else
+            {
+                /* Modify specified name to be processor specific name */
+                /* of the form "AppName.Name"                          */
+                CFE_ES_FormCDSName(CDSName, Name, ThisAppId);
+
+                /* Create CDS and designate it as NOT being a Critical Table */
+                Status = CFE_ES_RegisterCDSEx(CDSHandlePtr, BlockSize, CDSName, false);
+
+                /* If size is unacceptable, log it */
+                if (Status == CFE_ES_CDS_INVALID_SIZE)
+                {
+                    CFE_ES_WriteToSysLog("CFE_CDS:Register-CDS %s has invalid size (%lu)\n", Name, (unsigned long)BlockSize);
+                }
+            }
         }
     }
 
@@ -1875,6 +1899,11 @@ CFE_Status_t CFE_ES_GetCDSBlockName(char *BlockName, CFE_ES_CDSHandle_t BlockId,
 */
 int32 CFE_ES_CopyToCDS(CFE_ES_CDSHandle_t Handle, void *DataToCopy)
 {
+    if (DataToCopy == NULL)
+    {
+        return CFE_ES_BAD_ARGUMENT;
+    }
+
     return CFE_ES_CDSBlockWrite(Handle, DataToCopy);
 } /* End of CFE_ES_CopyToCDS() */
 
@@ -1886,6 +1915,11 @@ int32 CFE_ES_CopyToCDS(CFE_ES_CDSHandle_t Handle, void *DataToCopy)
 */
 int32 CFE_ES_RestoreFromCDS(void *RestoreToMemory, CFE_ES_CDSHandle_t Handle)
 {
+    if (RestoreToMemory == NULL)
+    {
+        return CFE_ES_BAD_ARGUMENT;
+    }
+    
     return CFE_ES_CDSBlockRead(RestoreToMemory, Handle);
 } /* End of CFE_ES_RestoreFromCDS() */
 
diff --git a/fsw/cfe-core/src/es/cfe_es_mempool.c b/fsw/cfe-core/src/es/cfe_es_mempool.c
index 5832b128d..66a833a42 100644
--- a/fsw/cfe-core/src/es/cfe_es_mempool.c
+++ b/fsw/cfe-core/src/es/cfe_es_mempool.c
@@ -411,6 +411,11 @@ int32 CFE_ES_GetPoolBuf(CFE_ES_MemPoolBuf_t *BufPtr,
     CFE_ES_MemPoolRecord_t *PoolRecPtr;
     size_t   DataOffset;
 
+    if (BufPtr == NULL)
+    {
+        return CFE_ES_BAD_ARGUMENT;
+    }
+
     PoolRecPtr = CFE_ES_LocateMemPoolRecordByID(Handle);
 
     /* basic sanity check */
@@ -473,6 +478,11 @@ int32 CFE_ES_GetPoolBufInfo(CFE_ES_MemHandle_t   Handle,
     size_t   DataOffset;
     size_t   DataSize;
 
+    if (BufPtr == NULL)
+    {
+        return CFE_ES_BAD_ARGUMENT;
+    }
+
     PoolRecPtr = CFE_ES_LocateMemPoolRecordByID(Handle);
 
     /* basic sanity check */
@@ -527,6 +537,11 @@ int32 CFE_ES_PutPoolBuf(CFE_ES_MemHandle_t   Handle,
     size_t   DataOffset;
     int32 Status;
 
+    if (BufPtr == NULL)
+    {
+        return CFE_ES_BAD_ARGUMENT;
+    }
+
     PoolRecPtr = CFE_ES_LocateMemPoolRecordByID(Handle);
 
     /* basic sanity check */
@@ -605,6 +620,11 @@ int32 CFE_ES_GetMemPoolStats(CFE_ES_MemPoolStats_t *BufPtr,
     uint16 NumBuckets;
     uint16 Idx;
 
+    if (BufPtr == NULL)
+    {
+        return CFE_ES_BAD_ARGUMENT;
+    }
+
     PoolRecPtr = CFE_ES_LocateMemPoolRecordByID(Handle);
 
     /* basic sanity check */
diff --git a/fsw/cfe-core/src/evs/cfe_evs.c b/fsw/cfe-core/src/evs/cfe_evs.c
index f3fb70b34..ac6c32318 100644
--- a/fsw/cfe-core/src/evs/cfe_evs.c
+++ b/fsw/cfe-core/src/evs/cfe_evs.c
@@ -154,6 +154,10 @@ int32 CFE_EVS_SendEvent (uint16 EventID, uint16 EventType, const char *Spec, ...
    va_list            Ptr;
    EVS_AppData_t     *AppDataPtr;
 
+   if(Spec == NULL){
+      return CFE_EVS_INVALID_PARAMETER;
+   }
+
    /* Query and verify the caller's AppID */
    Status = EVS_GetCurrentContext(&AppDataPtr, &AppID);
    if (Status == CFE_SUCCESS)
@@ -190,6 +194,10 @@ int32 CFE_EVS_SendEventWithAppID (uint16 EventID, uint16 EventType, CFE_ES_AppId
    va_list            Ptr;
    EVS_AppData_t     *AppDataPtr;
 
+   if(Spec == NULL){
+      return CFE_EVS_INVALID_PARAMETER;
+   }
+
    AppDataPtr = EVS_GetAppDataByID (AppID);
    if (AppDataPtr == NULL)
    {
@@ -225,6 +233,10 @@ int32 CFE_EVS_SendTimedEvent (CFE_TIME_SysTime_t Time, uint16 EventID, uint16 Ev
    va_list            Ptr;
    EVS_AppData_t     *AppDataPtr;
 
+   if(Spec == NULL){
+      return CFE_EVS_INVALID_PARAMETER;
+   }
+
    /* Query and verify the caller's AppID */
    Status = EVS_GetCurrentContext(&AppDataPtr, &AppID);
    if (Status == CFE_SUCCESS)
diff --git a/fsw/cfe-core/src/fs/cfe_fs_api.c b/fsw/cfe-core/src/fs/cfe_fs_api.c
index 4f83e5f13..5f00d21e0 100644
--- a/fsw/cfe-core/src/fs/cfe_fs_api.c
+++ b/fsw/cfe-core/src/fs/cfe_fs_api.c
@@ -50,6 +50,11 @@ int32 CFE_FS_ReadHeader(CFE_FS_Header_t *Hdr, osal_id_t FileDes)
 {
     int32   Result;
     int32   EndianCheck = 0x01020304;
+
+    if (Hdr == NULL)
+    {
+        return CFE_FS_BAD_ARGUMENT;
+    }
     
     /*
     ** Ensure that we are at the start of the file...
@@ -81,9 +86,16 @@ int32 CFE_FS_ReadHeader(CFE_FS_Header_t *Hdr, osal_id_t FileDes)
 */
 void CFE_FS_InitHeader(CFE_FS_Header_t *Hdr, const char *Description, uint32 SubType)
 {
-   memset(Hdr, 0, sizeof(CFE_FS_Header_t));
-   strncpy((char *)Hdr->Description, Description, sizeof(Hdr->Description) - 1);
-   Hdr->SubType = SubType;
+   if(Hdr == NULL || Description == NULL)
+   {
+        CFE_ES_WriteToSysLog("CFE_FS:InitHeader-Failed invalid arguments\n");
+   }
+   else
+   {
+        memset(Hdr, 0, sizeof(CFE_FS_Header_t));
+        strncpy((char *)Hdr->Description, Description, sizeof(Hdr->Description) - 1);
+        Hdr->SubType = SubType;
+   }
 }
 
 /*
@@ -96,6 +108,11 @@ int32 CFE_FS_WriteHeader(osal_id_t FileDes, CFE_FS_Header_t *Hdr)
     int32   EndianCheck = 0x01020304;
     CFE_ES_AppId_t AppID;
 
+    if (Hdr == NULL)
+	{
+		return CFE_FS_BAD_ARGUMENT;
+	}
+
     /*
     ** Ensure that we are at the start of the file...
     */
diff --git a/fsw/cfe-core/src/inc/cfe_error.h b/fsw/cfe-core/src/inc/cfe_error.h
index 872c89f03..4b1231b10 100644
--- a/fsw/cfe-core/src/inc/cfe_error.h
+++ b/fsw/cfe-core/src/inc/cfe_error.h
@@ -1325,6 +1325,14 @@ typedef int32 CFE_Status_t;
 */
 #define CFE_TBL_ERR_ACCESS              ((int32)0xcc00002c)
 
+/**
+ * @brief Bad Argument
+ *
+ *  A parameter given by a caller to a Table API did not pass 
+ *  validation checks.
+ *
+ */
+#define CFE_TBL_BAD_ARGUMENT            ((int32)0xcc00002d)
 
 /**
  * @brief Not Implemented
@@ -1400,6 +1408,15 @@ typedef int32 CFE_Status_t;
  *
  */
 #define CFE_TIME_CALLBACK_NOT_REGISTERED ((int32)0xce000004)
+
+/**
+ * @brief Bad Argument
+ *
+ *  A parameter given by a caller to a TIME Services API did not pass 
+ *  validation checks.
+ *
+ */
+#define CFE_TIME_BAD_ARGUMENT            ((int32)0xce000005)
 /**@}*/
 
 
diff --git a/fsw/cfe-core/src/sb/cfe_sb_api.c b/fsw/cfe-core/src/sb/cfe_sb_api.c
index 772a84e53..bd4908ef3 100644
--- a/fsw/cfe-core/src/sb/cfe_sb_api.c
+++ b/fsw/cfe-core/src/sb/cfe_sb_api.c
@@ -2147,7 +2147,13 @@ CFE_SB_Buffer_t *CFE_SB_ZeroCopyGetPtr(size_t MsgSize,
     CFE_ES_GetAppID(&AppId);
     zcd->AppID     = AppId;
 
-    (*BufferHandle) = (CFE_SB_ZeroCopyHandle_t) zcd;
+    if(BufferHandle != NULL){
+        (*BufferHandle) = (CFE_SB_ZeroCopyHandle_t) zcd;        
+    }
+    else
+    {
+        CFE_ES_WriteToSysLog(" CFE_SB:ZeroCopyGetPtr-BufferHandle is NULL\n");
+    }    
 
     /* Initialize the buffer descriptor structure. */
     bd->UseCount  = 1;
diff --git a/fsw/cfe-core/src/sb/cfe_sb_util.c b/fsw/cfe-core/src/sb/cfe_sb_util.c
index 654f5f47b..119c067b7 100644
--- a/fsw/cfe-core/src/sb/cfe_sb_util.c
+++ b/fsw/cfe-core/src/sb/cfe_sb_util.c
@@ -39,6 +39,7 @@
 #include "osapi.h"
 #include "cfe_error.h"
 #include "cfe_msg_api.h"
+#include "cfe_es.h"
 
 #include <string.h>
 
@@ -75,6 +76,11 @@ size_t CFE_SB_MsgHdrSize(const CFE_MSG_Message_t *MsgPtr)
     bool           hassechdr = false;
     CFE_MSG_Type_t type = CFE_MSG_Type_Invalid;
 
+    if (MsgPtr == NULL)
+    {
+        return CFE_SB_BAD_ARGUMENT;
+    }
+
     CFE_MSG_GetHasSecondaryHeader(MsgPtr, &hassechdr);
     CFE_MSG_GetType(MsgPtr, &type);
 
@@ -106,6 +112,11 @@ void *CFE_SB_GetUserData(CFE_MSG_Message_t *MsgPtr)
     uint8           *BytePtr;
     size_t          HdrSize;
 
+    if(MsgPtr == NULL){
+        CFE_ES_WriteToSysLog("CFE_SB:GetUserData-Failed invalid arguments\n");
+        return 0;
+    }
+
     BytePtr = (uint8 *)MsgPtr;
     HdrSize = CFE_SB_MsgHdrSize(MsgPtr);
 
@@ -121,6 +132,11 @@ size_t CFE_SB_GetUserDataLength(const CFE_MSG_Message_t *MsgPtr)
     CFE_MSG_Size_t TotalMsgSize;
     size_t HdrSize;
 
+    if (MsgPtr == NULL)
+    {
+        return CFE_SB_BAD_ARGUMENT;
+    }
+
     CFE_MSG_GetSize(MsgPtr, &TotalMsgSize);
     HdrSize = CFE_SB_MsgHdrSize(MsgPtr);
 
@@ -136,11 +152,16 @@ void CFE_SB_SetUserDataLength(CFE_MSG_Message_t *MsgPtr, size_t DataLength)
     CFE_MSG_Size_t TotalMsgSize;
     size_t HdrSize;
 
-    HdrSize = CFE_SB_MsgHdrSize(MsgPtr);
-    TotalMsgSize = HdrSize + DataLength;
+    if(MsgPtr == NULL){
+        CFE_ES_WriteToSysLog("CFE_SB:SetUserDataLength-Failed invalid arguments\n");
+    }
+    else
+    {
+        HdrSize = CFE_SB_MsgHdrSize(MsgPtr);
+        TotalMsgSize = HdrSize + DataLength;
     
-    CFE_MSG_SetSize(MsgPtr, TotalMsgSize);
-
+        CFE_MSG_SetSize(MsgPtr, TotalMsgSize);
+    }
 }/* end CFE_SB_SetUserDataLength */
 
 #ifndef CFE_OMIT_DEPRECATED_6_8
@@ -288,7 +309,7 @@ int32 CFE_SB_MessageStringGet(char *DestStringPtr, const char *SourceStringPtr,
      * Cannot terminate the string, since there is no place for the NUL
      * In this case, do nothing
      */
-    if (DestMaxSize == 0)
+    if (DestMaxSize == 0 || DestStringPtr == NULL )
     {
         Result = CFE_SB_BAD_ARGUMENT;
     }
@@ -335,28 +356,35 @@ int32 CFE_SB_MessageStringSet(char *DestStringPtr, const char *SourceStringPtr,
 {
     int32 Result;
 
-    Result = 0;
-
-    while (SourceMaxSize > 0 && *SourceStringPtr != 0 && DestMaxSize > 0)
+    if (SourceStringPtr == NULL || DestStringPtr == NULL )
     {
-        *DestStringPtr = *SourceStringPtr;
-        ++DestStringPtr;
-        ++SourceStringPtr;
-        ++Result;
-        --DestMaxSize;
-        --SourceMaxSize;
+        Result = CFE_SB_BAD_ARGUMENT;
     }
-
-    /*
-     * Pad the remaining space with NUL chars,
-     * but this should NOT be included in the final size
-     */
-    while (DestMaxSize > 0)
+    else
     {
-        /* Put the NUL in the last character */
-        *DestStringPtr = 0;
-        ++DestStringPtr;
-        --DestMaxSize;
+        Result = 0;
+
+        while (SourceMaxSize > 0 && *SourceStringPtr != 0 && DestMaxSize > 0)
+        {
+            *DestStringPtr = *SourceStringPtr;
+            ++DestStringPtr;
+            ++SourceStringPtr;
+            ++Result;
+            --DestMaxSize;
+            --SourceMaxSize;
+        }
+
+        /*
+        * Pad the remaining space with NUL chars,
+        * but this should NOT be included in the final size
+        */
+        while (DestMaxSize > 0)
+        {
+            /* Put the NUL in the last character */
+            *DestStringPtr = 0;
+            ++DestStringPtr;
+            --DestMaxSize;
+        }
     }
 
     return Result;
diff --git a/fsw/cfe-core/src/tbl/cfe_tbl_api.c b/fsw/cfe-core/src/tbl/cfe_tbl_api.c
index 6e70c020e..1b58a2e69 100644
--- a/fsw/cfe-core/src/tbl/cfe_tbl_api.c
+++ b/fsw/cfe-core/src/tbl/cfe_tbl_api.c
@@ -66,6 +66,11 @@ int32 CFE_TBL_Register( CFE_TBL_Handle_t *TblHandlePtr,
     char                        TblName[CFE_TBL_MAX_FULL_NAME_LEN] = {""};
     CFE_TBL_Handle_t            AccessIndex;
 
+    if (TblHandlePtr == NULL || Name == NULL)
+    {
+        return CFE_TBL_BAD_ARGUMENT;
+    }
+
     /* Check to make sure calling application is legit */
     Status = CFE_ES_GetAppID(&ThisAppId);
 
@@ -522,6 +527,11 @@ int32 CFE_TBL_Share( CFE_TBL_Handle_t *TblHandlePtr,
     CFE_TBL_RegistryRec_t      *RegRecPtr = NULL;
     char    AppName[OS_MAX_API_NAME] = {"UNKNOWN"};
 
+    if (TblHandlePtr == NULL || TblName == NULL)
+    {
+        return CFE_TBL_BAD_ARGUMENT;
+    }
+    
     /* Get a valid Application ID for calling App */
     Status = CFE_ES_GetAppID(&ThisAppId);
 
@@ -692,6 +702,11 @@ int32 CFE_TBL_Load( CFE_TBL_Handle_t TblHandle,
     char                        AppName[OS_MAX_API_NAME] = {"UNKNOWN"};
     bool                        FirstTime = false;
 
+    if (SrcDataPtr == NULL)
+    {
+        return CFE_TBL_BAD_ARGUMENT;
+    }
+
     /* Verify access rights and get a valid Application ID for calling App */
     Status = CFE_TBL_ValidateAccess(TblHandle, &ThisAppId);
 
@@ -1000,6 +1015,11 @@ int32 CFE_TBL_GetAddress( void **TblPtr,
     int32   Status;
     CFE_ES_AppId_t  ThisAppId;
 
+    if (TblPtr == NULL)
+    {
+        return CFE_TBL_BAD_ARGUMENT;
+    }
+
     /* Assume failure at returning the table address */
     *TblPtr = NULL;
 
@@ -1066,6 +1086,11 @@ int32 CFE_TBL_GetAddresses( void **TblPtrs[],
     int32   Status;
     CFE_ES_AppId_t   ThisAppId;
 
+     if (TblPtrs == NULL)
+    {
+        return CFE_TBL_BAD_ARGUMENT;
+    }
+
     /* Assume failure at returning the table addresses */
     for (i=0; i<NumTables; i++)
     {
@@ -1388,6 +1413,10 @@ int32 CFE_TBL_GetInfo( CFE_TBL_Info_t *TblInfoPtr, const char *TblName )
     CFE_TBL_RegistryRec_t   *RegRecPtr;
     CFE_TBL_Handle_t         HandleIterator;
 
+    if(TblInfoPtr == NULL || TblName == NULL){
+        return CFE_TBL_BAD_ARGUMENT;
+    }
+
     RegIndx = CFE_TBL_FindTableInRegistry(TblName);
 
     /* If we found the table, then extract the information from the Registry */
diff --git a/fsw/cfe-core/src/time/cfe_time_api.c b/fsw/cfe-core/src/time/cfe_time_api.c
index 2bbfa92e6..bab936009 100644
--- a/fsw/cfe-core/src/time/cfe_time_api.c
+++ b/fsw/cfe-core/src/time/cfe_time_api.c
@@ -547,6 +547,12 @@ void CFE_TIME_Print(char *PrintBuffer, CFE_TIME_SysTime_t TimeToPrint)
 
     bool StillCountingYears = true;
 
+    if (PrintBuffer == NULL)
+    {
+        CFE_ES_WriteToSysLog("CFE_TIME:Print-Failed invalid arguments\n");
+        return;
+    }
+
     /*
     ** Convert the cFE time (offset from epoch) into calendar time...
     */
@@ -693,6 +699,11 @@ int32  CFE_TIME_RegisterSynchCallback(CFE_TIME_SynchCallbackPtr_t CallbackFuncPt
     CFE_ES_AppId_t AppId;
     uint32 AppIndex;
 
+    if (CallbackFuncPtr == NULL)
+    {
+        return CFE_TIME_BAD_ARGUMENT;
+    }
+
     Status = CFE_ES_GetAppID(&AppId);
     if (Status == CFE_SUCCESS)
     {
@@ -726,6 +737,11 @@ int32  CFE_TIME_UnregisterSynchCallback(CFE_TIME_SynchCallbackPtr_t CallbackFunc
     CFE_ES_AppId_t AppId;
     uint32 AppIndex;
 
+    if (CallbackFuncPtr == NULL)
+    {
+        return CFE_TIME_BAD_ARGUMENT;
+    }
+
     Status = CFE_ES_GetAppID(&AppId);
     if (Status == CFE_SUCCESS)
     {