diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index f0c7aad..06837ac 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -5590,7 +5590,8 @@
 
     // Special handling of "ff" which acts as a short form of
     // "fileformat", as "ff" is not a substring of it.
-    if (STRCMP(xp->xp_pattern, "ff") == 0)
+    if (xp->xp_pattern_len == 2
+	    && STRNCMP(xp->xp_pattern, "ff", xp->xp_pattern_len) == 0)
     {
 	*matches = ALLOC_MULT(char_u *, 1);
 	if (*matches == NULL)