diff --git a/share/namespace.go b/share/namespace.go
index e7ed7dc0d6..df4ad74058 100644
--- a/share/namespace.go
+++ b/share/namespace.go
@@ -20,13 +20,13 @@ var (
 	// MinSecondaryReservedNamespace is the lowest secondary reserved namespace
 	// reserved for protocol use. Namespaces higher than this are reserved for
 	// protocol use.
-	MinSecondaryReservedNamespace = Namespace(appns.MinSecondaryReservedNamespace.Bytes())
-	ParitySharesNamespace         = Namespace(appns.ParitySharesNamespace.Bytes())
-	TailPaddingNamespace          = Namespace(appns.TailPaddingNamespace.Bytes())
-	ReservedPaddingNamespace      = Namespace(appns.PrimaryReservedPaddingNamespace.Bytes())
-	TxNamespace                   = Namespace(appns.TxNamespace.Bytes())
-	PayForBlobNamespace           = Namespace(appns.PayForBlobNamespace.Bytes())
-	ISRNamespace                  = Namespace(appns.IntermediateStateRootsNamespace.Bytes())
+	MinSecondaryReservedNamespace   = Namespace(appns.MinSecondaryReservedNamespace.Bytes())
+	ParitySharesNamespace           = Namespace(appns.ParitySharesNamespace.Bytes())
+	TailPaddingNamespace            = Namespace(appns.TailPaddingNamespace.Bytes())
+	PrimaryReservedPaddingNamespace = Namespace(appns.PrimaryReservedPaddingNamespace.Bytes())
+	TxNamespace                     = Namespace(appns.TxNamespace.Bytes())
+	PayForBlobNamespace             = Namespace(appns.PayForBlobNamespace.Bytes())
+	ISRNamespace                    = Namespace(appns.IntermediateStateRootsNamespace.Bytes())
 )
 
 // Namespace represents namespace of a Share.
diff --git a/share/namespace_test.go b/share/namespace_test.go
index 7c18d233c8..786441b043 100644
--- a/share/namespace_test.go
+++ b/share/namespace_test.go
@@ -173,6 +173,16 @@ func TestValidateForBlob(t *testing.T) {
 			ns:      append([]byte{appns.NamespaceVersionMax}, bytes.Repeat([]byte{0x0}, appns.NamespaceIDSize)...),
 			wantErr: true,
 		},
+		{
+			name:    "invalid blob namespace: primary reserved namespace",
+			ns:      primaryReservedNamespace(0x10),
+			wantErr: true,
+		},
+		{
+			name:    "invalid blob namespace: secondary reserved namespace",
+			ns:      secondaryReservedNamespace(0x10),
+			wantErr: true,
+		},
 	}
 
 	for _, tc := range testCases {
@@ -186,5 +196,21 @@ func TestValidateForBlob(t *testing.T) {
 			assert.NoError(t, err)
 		})
 	}
+}
+
+func primaryReservedNamespace(lastByte byte) Namespace {
+	result := make([]byte, NamespaceSize)
+	result = append(result, appns.NamespaceVersionZero)
+	result = append(result, appns.NamespaceVersionZeroPrefix...)
+	result = append(result, bytes.Repeat([]byte{0x0}, appns.NamespaceVersionZeroIDSize-1)...)
+	result = append(result, lastByte)
+	return result
+}
 
+func secondaryReservedNamespace(lastByte byte) Namespace {
+	result := make([]byte, NamespaceSize)
+	result = append(result, appns.NamespaceVersionMax)
+	result = append(result, bytes.Repeat([]byte{0xFF}, appns.NamespaceIDSize-1)...)
+	result = append(result, lastByte)
+	return result
 }