diff --git a/plan9/mkerrors.sh b/plan9/mkerrors.sh
index 85309c4a5b..526d04ab68 100755
--- a/plan9/mkerrors.sh
+++ b/plan9/mkerrors.sh
@@ -126,7 +126,7 @@ errors=$(
 signals=$(
 	echo '#include <signal.h>' | $CC -x c - -E -dM $ccflags |
 	awk '$1=="#define" && $2 ~ /^SIG[A-Z0-9]+$/ { print $2 }' |
-	egrep -v '(SIGSTKSIZE|SIGSTKSZ|SIGRT)' |
+	grep -v 'SIGSTKSIZE\|SIGSTKSZ\|SIGRT' |
 	sort
 )
 
@@ -136,7 +136,7 @@ echo '#include <errno.h>' | $CC -x c - -E -dM $ccflags |
 	sort >_error.grep
 echo '#include <signal.h>' | $CC -x c - -E -dM $ccflags |
 	awk '$1=="#define" && $2 ~ /^SIG[A-Z0-9]+$/ { print "^\t" $2 "[ \t]*=" }' |
-	egrep -v '(SIGSTKSIZE|SIGSTKSZ|SIGRT)' |
+	grep -v 'SIGSTKSIZE\|SIGSTKSZ\|SIGRT' |
 	sort >_signal.grep
 
 echo '// mkerrors.sh' "$@"
diff --git a/unix/mkerrors.sh b/unix/mkerrors.sh
index 2ab44aa659..7456d9ddde 100755
--- a/unix/mkerrors.sh
+++ b/unix/mkerrors.sh
@@ -642,7 +642,7 @@ errors=$(
 signals=$(
 	echo '#include <signal.h>' | $CC -x c - -E -dM $ccflags |
 	awk '$1=="#define" && $2 ~ /^SIG[A-Z0-9]+$/ { print $2 }' |
-	egrep -v '(SIGSTKSIZE|SIGSTKSZ|SIGRT|SIGMAX64)' |
+	grep -v 'SIGSTKSIZE\|SIGSTKSZ\|SIGRT\|SIGMAX64' |
 	sort
 )
 
@@ -652,7 +652,7 @@ echo '#include <errno.h>' | $CC -x c - -E -dM $ccflags |
 	sort >_error.grep
 echo '#include <signal.h>' | $CC -x c - -E -dM $ccflags |
 	awk '$1=="#define" && $2 ~ /^SIG[A-Z0-9]+$/ { print "^\t" $2 "[ \t]*=" }' |
-	egrep -v '(SIGSTKSIZE|SIGSTKSZ|SIGRT|SIGMAX64)' |
+	grep -v 'SIGSTKSIZE\|SIGSTKSZ\|SIGRT\|SIGMAX64' |
 	sort >_signal.grep
 
 echo '// mkerrors.sh' "$@"