diff --git a/mk/pp.mk b/mk/pp.mk
index aaef946bb29..21ed07d34b7 100644
--- a/mk/pp.mk
+++ b/mk/pp.mk
@@ -17,7 +17,11 @@ reformat: $(SREQ1)
 	for i in $(PP_INPUTS_FILTERED);  \
     do $(call CFG_RUN_TARG,stage1,stage1/rustc$(X)) \
        --pretty normal $$i >$$i.tmp; \
-    if cmp --silent $$i.tmp $$i; \
-        then echo no changes to $$i; rm $$i.tmp; \
-        else mv $$i.tmp $$i; fi \
+    if [ $$? -ne 0 ]; \
+        then echo failed to print $$i; rm $$i.tmp; \
+        else if cmp --silent $$i.tmp $$i; \
+            then echo no changes to $$i; rm $$i.tmp; \
+            else echo reformated $$i; mv $$i.tmp $$i; \
+        fi; \
+    fi; \
     done