diff --git a/src/common/cvt.cpp b/src/common/cvt.cpp
index 5c0938fe66..bc9eeaaf88 100644
--- a/src/common/cvt.cpp
+++ b/src/common/cvt.cpp
@@ -3536,7 +3536,7 @@ static void hex_to_value(const char*& string, const char* end, RetPtr* retValue)
 	int nibble = ((end - string) & 1);
 	char ch;
 
-	while ((DIGIT((ch = UPPER(*string)))) || ((ch >= 'A') && (ch <= 'F')))
+	while ((string < end) && ((DIGIT((ch = UPPER(*string)))) || ((ch >= 'A') && (ch <= 'F'))))
 	{
 		// Now convert the character to a nibble
 		SSHORT c;