diff --git a/tests/r5rs-tests.scm b/tests/r5rs-tests.scm
index 0a65fdd1..b056be49 100644
--- a/tests/r5rs-tests.scm
+++ b/tests/r5rs-tests.scm
@@ -247,7 +247,7 @@
 
 (test "100" (number->string 256 16))
 
-(test "FF" (number->string 255 16))
+(test "ff" (number->string 255 16))
 
 (test "177" (number->string 127 8))