diff --git a/bin/expr/Makefile b/bin/expr/Makefile
index a1f6cbf2109..1d741b7e0b6 100644
--- a/bin/expr/Makefile
+++ b/bin/expr/Makefile
@@ -6,6 +6,9 @@ PROG=	expr
 SRCS=	expr.y
 YFLAGS=
 
+# expr relies on signed integer wrapping
+CFLAGS+= -fwrapv
+
 NO_WMISSING_VARIABLE_DECLARATIONS=
 
 .if ${MK_TESTS} != "no"