diff --git a/ChangeLog b/ChangeLog
index 58dcf0c091..3dcf4b30b0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-11-07  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
+
+	* support/support_test_compare_string.c
+	(support_test_compare_string): Fix printf format.
+
 2018-11-07  Florian Weimer  <fweimer@redhat.com>
 
 	Implement TEST_COMPARE_STRING.
diff --git a/support/support_test_compare_string.c b/support/support_test_compare_string.c
index 9958aaeec1..a76ba8eda7 100644
--- a/support/support_test_compare_string.c
+++ b/support/support_test_compare_string.c
@@ -77,7 +77,7 @@ support_test_compare_string (const char *left, const char *right,
       support_record_failure ();
       printf ("%s:%d: error: blob comparison failed\n", file, line);
       if (left_length == right_length && right != NULL && left != NULL)
-        printf ("  string length: %lu bytes\n", left_length);
+        printf ("  string length: %zu bytes\n", left_length);
       else
         {
           report_length ("left", left, left_length);