diff --git a/lib/fko_encode.c b/lib/fko_encode.c
index 2adb42ff..5a28b6ec 100644
--- a/lib/fko_encode.c
+++ b/lib/fko_encode.c
@@ -41,9 +41,12 @@
 static int
 append_b64(char* tbuf, char *str)
 {
-    int   len = strlen(str);
+    int   len = strnlen(str, MAX_SPA_ENCODED_MSG_SIZE);
     char *bs;
 
+    if(len >= MAX_SPA_ENCODED_MSG_SIZE)
+        return(FKO_ERROR_INVALID_DATA);
+
     bs = malloc(((len/3)*4)+8);
     if(bs == NULL)
         return(FKO_ERROR_MEMORY_ALLOCATION);