diff --git a/libavutil/mem.c b/libavutil/mem.c
index 741450b..1ce0b77 100644
--- a/libavutil/mem.c
+++ b/libavutil/mem.c
@@ -113,7 +113,9 @@
     //FIXME this isn't aligned correctly, though it probably isn't needed
     if(!ptr) return av_malloc(size);
     diff= ((char*)ptr)[-1];
-    return (char*)realloc((char*)ptr - diff, size + diff) + diff;
+    ptr= realloc((char*)ptr - diff, size + diff);
+    if(ptr) ptr = (char*)ptr + diff;
+    return ptr;
 #else
     return realloc(ptr, size);
 #endif