diff --git a/src/util/FFstrbuf.c b/src/util/FFstrbuf.c
index 10395676b..f54b2da53 100644
--- a/src/util/FFstrbuf.c
+++ b/src/util/FFstrbuf.c
@@ -293,7 +293,7 @@ void ffStrbufTrimLeft(FFstrbuf* strbuf, char c)
     if(index == 0)
         return;
 
-    memmove(strbuf->chars, strbuf->chars + index, index);
+    memmove(strbuf->chars, strbuf->chars + index, strbuf->length - index);
     strbuf->length -= index;
     strbuf->chars[strbuf->length] = '\0';
 }