diff --git a/src/configure b/src/configure
index 6068fe968..15c53f57e 100755
--- a/src/configure
+++ b/src/configure
@@ -2512,14 +2512,14 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $OSVER" >&5
 $as_echo "$OSVER" >&6; }
 
-CFLAGS=""
+CFLAGS="$CFLAGS"
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for perf_event workaround level" >&5
 $as_echo_n "checking for perf_event workaround level... " >&6; }
 
 # Check whether --with-assumed_kernel was given.
 if test "${with_assumed_kernel+set}" = set; then :
-  withval=$with_assumed_kernel; assumed_kernel=$withval; CFLAGS="-DASSUME_KERNEL=\\\"$with_assumed_kernel\\\""
+  withval=$with_assumed_kernel; assumed_kernel=$withval; CFLAGS="$CFLAGS -DASSUME_KERNEL=\\\"$with_assumed_kernel\\\""
 else
   assumed_kernel="autodetect"
 
diff --git a/src/configure.in b/src/configure.in
index 827d23170..1cde6d8b5 100644
--- a/src/configure.in
+++ b/src/configure.in
@@ -69,13 +69,13 @@ AC_ARG_WITH(OSVER,
             fi ])
 AC_MSG_RESULT($OSVER)
 
-CFLAGS=""
+CFLAGS="$CFLAGS"
 
 AC_MSG_CHECKING(for perf_event workaround level)
 AC_ARG_WITH(assumed_kernel,
             [AS_HELP_STRING([--with-assumed-kernel=<ver>],
             [Assume kernel version is <ver> for purposes of workarounds])],
-		[assumed_kernel=$withval; CFLAGS="-DASSUME_KERNEL=\\\"$with_assumed_kernel\\\""],
+		[assumed_kernel=$withval; CFLAGS="$CFLAGS -DASSUME_KERNEL=\\\"$with_assumed_kernel\\\""],
                 [assumed_kernel="autodetect"]
 		)		
 AC_MSG_RESULT($assumed_kernel)