diff --git a/Makefile.inc1 b/Makefile.inc1
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -731,7 +731,7 @@
 		SSP_CFLAGS= \
 		MK_HTML=no NO_LINT=yes MK_MAN=no MK_MAN_UTILS=yes \
 		-DNO_PIC MK_PROFILE=no -DNO_SHARED \
-		-DNO_CPU_CFLAGS MK_WARNS=no MK_CTF=no \
+		-DNO_CPU_CFLAGS -DNO_WERROR MK_CTF=no \
 		MK_CLANG_EXTRAS=no MK_CLANG_FORMAT=no MK_CLANG_FULL=no \
 		MK_LLDB=no MK_RETPOLINE=no MK_TESTS=no \
 		MK_INCLUDES=yes
@@ -752,7 +752,7 @@
 		BWPHASE=${.TARGET:C,^_,,} \
 		SSP_CFLAGS= \
 		-DNO_LINT \
-		-DNO_CPU_CFLAGS MK_WARNS=no MK_CTF=no \
+		-DNO_CPU_CFLAGS -DNO_WERROR MK_CTF=no \
 		MK_CLANG_EXTRAS=no MK_CLANG_FORMAT=no MK_CLANG_FULL=no \
 		MK_LLDB=no MK_RETPOLINE=no MK_TESTS=no
 
@@ -780,7 +780,7 @@
 		SSP_CFLAGS= \
 		MK_HTML=no -DNO_LINT MK_MAN=no \
 		-DNO_PIC MK_PROFILE=no -DNO_SHARED \
-		-DNO_CPU_CFLAGS MK_RETPOLINE=no MK_WARNS=no MK_CTF=no
+		-DNO_CPU_CFLAGS MK_RETPOLINE=no -DNO_WERROR MK_CTF=no
 
 # world stage
 WMAKEENV=	${CROSSENV} \
@@ -2748,7 +2748,7 @@
 	MK_SENDMAIL=no \
 	MK_SVNLITE=no \
 	MK_TESTS=no \
-	MK_WARNS=no \
+	-DNO_WERROR \
 	MK_ZFS=no
 
 .if make(native-xtools*) && \
@@ -3367,7 +3367,7 @@
 
 NOFUN=-DNO_FSCHG MK_HTML=no -DNO_LINT \
 	MK_MAN=no MK_NLS=no MK_PROFILE=no \
-	MK_KERBEROS=no MK_RESCUE=no MK_TESTS=no MK_WARNS=no \
+	MK_KERBEROS=no MK_RESCUE=no MK_TESTS=no -DNO_WERROR \
 	TARGET=${TARGET} TARGET_ARCH=${TARGET_ARCH} \
 	CPUTYPE=${XDEV_CPUTYPE}
 
diff --git a/Makefile.libcompat b/Makefile.libcompat
--- a/Makefile.libcompat
+++ b/Makefile.libcompat
@@ -104,7 +104,7 @@
 	    OBJROOT='$${OBJTOP}/' \
 	    MAKEOBJDIRPREFIX= \
 	    DIRPRFX=${_dir}/ -DNO_LINT -DNO_CPU_CFLAGS \
-	    MK_CTF=no MK_RETPOLINE=no MK_WARNS=no \
+	    MK_CTF=no MK_RETPOLINE=no -DNO_WERROR \
 	    ${_t}
 .endfor
 .endfor
diff --git a/targets/pseudo/bootstrap-tools/Makefile b/targets/pseudo/bootstrap-tools/Makefile
--- a/targets/pseudo/bootstrap-tools/Makefile
+++ b/targets/pseudo/bootstrap-tools/Makefile
@@ -42,7 +42,7 @@
 		SSP_CFLAGS= \
 		MK_HTML=no NO_LINT=yes MK_MAN=no \
 		-DNO_PIC MK_PROFILE=no -DNO_SHARED \
-		-DNO_CPU_CFLAGS MK_WARNS=no MK_CTF=no \
+		-DNO_CPU_CFLAGS -DNO_WERROR MK_CTF=no \
 		MK_CLANG_EXTRAS=no MK_CLANG_FORMAT=no MK_CLANG_FULL=no \
 		MK_LLDB=no MK_TESTS=no \
 		MK_INCLUDES=yes