1 files changed, 1 insertions, 1 deletions
diff --git a/src/cmp.c b/src/cmp.c
index 2620b0f..2aba127 100644
--- a/src/cmp.c
+++ b/src/cmp.c
@@ -51,7 +51,7 @@
 
 static int cmp (void);
 static off_t file_position (int);
-static size_t block_compare (word const *, word const *);
+static size_t block_compare (word const *, word const *) _GL_ATTRIBUTE_PURE;
 static size_t block_compare_and_count (word const *, word const *, off_t *);
 static void sprintc (char *, unsigned char);