diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 73ddaf0..2044324 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -554,7 +554,7 @@
 
 	is_kernel_mmap = memcmp(event->mmap.filename,
 				kmmap_prefix,
-				strlen(kmmap_prefix)) == 0;
+				strlen(kmmap_prefix) - 1) == 0;
 	if (event->mmap.filename[0] == '/' ||
 	    (!is_kernel_mmap && event->mmap.filename[0] == '[')) {