diff --git a/config/config.mk b/config/config.mk
index 2bb97999694..669c21277f1 100644
--- a/config/config.mk
+++ b/config/config.mk
@@ -45,9 +45,9 @@
 #
 
 # Define an include-at-most-once flag
-#ifdef INCLUDED_CONFIG_MK
-#$(error Don't include config.mk twice!)
-#endif
+ifdef INCLUDED_CONFIG_MK
+$(error Don't include config.mk twice!)
+endif
 INCLUDED_CONFIG_MK = 1
 
 EXIT_ON_ERROR = set -e; # Shell loops continue past errors without this.
diff --git a/js/src/config/config.mk b/js/src/config/config.mk
index 2bb97999694..669c21277f1 100644
--- a/js/src/config/config.mk
+++ b/js/src/config/config.mk
@@ -45,9 +45,9 @@
 #
 
 # Define an include-at-most-once flag
-#ifdef INCLUDED_CONFIG_MK
-#$(error Don't include config.mk twice!)
-#endif
+ifdef INCLUDED_CONFIG_MK
+$(error Don't include config.mk twice!)
+endif
 INCLUDED_CONFIG_MK = 1
 
 EXIT_ON_ERROR = set -e; # Shell loops continue past errors without this.
diff --git a/toolkit/crashreporter/google-breakpad/src/client/linux/crash_generation/Makefile.in b/toolkit/crashreporter/google-breakpad/src/client/linux/crash_generation/Makefile.in
index 17c2662d757..3ef204a51ff 100644
--- a/toolkit/crashreporter/google-breakpad/src/client/linux/crash_generation/Makefile.in
+++ b/toolkit/crashreporter/google-breakpad/src/client/linux/crash_generation/Makefile.in
@@ -58,7 +58,6 @@ FORCE_USE_PIC = 1
 
 include $(topsrcdir)/config/rules.mk
 ifeq ($(OS_ARCH),Linux)
-include $(topsrcdir)/config/config.mk
 # need this to suppress errors when compiling common/linux/eintr_wrapper.h
 OS_CXXFLAGS := $(filter-out -pedantic,$(OS_CXXFLAGS))
 endif