diff --git a/dict.c b/dict.c
index 5f71d55..a9ff53e 100644
--- a/dict.c
+++ b/dict.c
@@ -249,7 +249,7 @@ xmlDictAddString(xmlDictPtr dict, const xmlChar *name, unsigned int namelen) {
 #endif
     pool = dict->strings;
     while (pool != NULL) {
-	if (pool->end - pool->free > namelen)
+	if (pool->end > pool->free && (size_t)(pool->end - pool->free) > namelen)
 	    goto found_pool;
 	if (pool->size > size) size = pool->size;
         limit += pool->size;
@@ -317,7 +317,8 @@ xmlDictAddQString(xmlDictPtr dict, const xmlChar *prefix, unsigned int plen,
 #endif
     pool = dict->strings;
     while (pool != NULL) {
-	if (pool->end - pool->free > namelen + plen + 1)
+	if (pool->end > pool->free &&
+      (size_t)(pool->end - pool->free) > namelen + plen + 1)
 	    goto found_pool;
 	if (pool->size > size) size = pool->size;
         limit += pool->size;