diff --git a/make/bsd/makefiles/gcc.make b/make/bsd/makefiles/gcc.make
index 2cee1b0034ebe2474193828e30eb0fba06db210c..b742eb12992c57fb976c33fa5329c18466af4e69 100644
--- a/make/bsd/makefiles/gcc.make
+++ b/make/bsd/makefiles/gcc.make
@@ -168,12 +168,12 @@ endif
 # conversions which might affect the values. To avoid that, we need to turn
 # it off explicitly. 
 ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
-ACCEPTABLE_WARNINGS = -Wpointer-arith -Wsign-compare
+WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef
 else
-ACCEPTABLE_WARNINGS = -Wpointer-arith -Wconversion -Wsign-compare
+WARNING_FLAGS = -Wpointer-arith -Wconversion -Wsign-compare -Wundef
 endif
 
-CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(ACCEPTABLE_WARNINGS)
+CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(WARNING_FLAGS)
 # Special cases
 CFLAGS_WARN/BYFILE = $(CFLAGS_WARN/$@)$(CFLAGS_WARN/DEFAULT$(CFLAGS_WARN/$@)) 
 # XXXDARWIN: for _dyld_bind_fully_image_containing_address
diff --git a/make/linux/makefiles/gcc.make b/make/linux/makefiles/gcc.make
index 9ef83664535f441a94c0e036854b9440601e61e6..b2c4bdfa49163f7b42a9c25706bde11b235bd517 100644
--- a/make/linux/makefiles/gcc.make
+++ b/make/linux/makefiles/gcc.make
@@ -131,12 +131,12 @@ WARNINGS_ARE_ERRORS = -Werror
 # conversions which might affect the values. To avoid that, we need to turn
 # it off explicitly. 
 ifneq "$(shell expr \( $(CC_VER_MAJOR) \> 4 \) \| \( \( $(CC_VER_MAJOR) = 4 \) \& \( $(CC_VER_MINOR) \>= 3 \) \))" "0"
-ACCEPTABLE_WARNINGS = -Wpointer-arith -Wsign-compare
+WARNING_FLAGS = -Wpointer-arith -Wsign-compare -Wundef
 else
-ACCEPTABLE_WARNINGS = -Wpointer-arith -Wconversion -Wsign-compare
+WARNING_FLAGS = -Wpointer-arith -Wconversion -Wsign-compare -Wundef
 endif
 
-CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(ACCEPTABLE_WARNINGS)
+CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(WARNING_FLAGS)
 # Special cases
 CFLAGS_WARN/BYFILE = $(CFLAGS_WARN/$@)$(CFLAGS_WARN/DEFAULT$(CFLAGS_WARN/$@)) 
 
diff --git a/make/solaris/makefiles/gcc.make b/make/solaris/makefiles/gcc.make
index 66ab8c55d6ad6eb38148503da2e59fe2e8314bbc..e946d65d256574a6bbbf8526c8facb028c4b2152 100644
--- a/make/solaris/makefiles/gcc.make
+++ b/make/solaris/makefiles/gcc.make
@@ -118,8 +118,8 @@ endif
 # Compiler warnings are treated as errors 
 WARNINGS_ARE_ERRORS = -Werror 
 # Enable these warnings. See 'info gcc' about details on these options
-ADDITIONAL_WARNINGS = -Wpointer-arith -Wconversion -Wsign-compare 
-CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(ADDITIONAL_WARNINGS) 
+WARNING_FLAGS = -Wpointer-arith -Wconversion -Wsign-compare -Wundef
+CFLAGS_WARN/DEFAULT = $(WARNINGS_ARE_ERRORS) $(WARNING_FLAGS)
 # Special cases 
 CFLAGS_WARN/BYFILE = $(CFLAGS_WARN/$@)$(CFLAGS_WARN/DEFAULT$(CFLAGS_WARN/$@))