diff --git a/lang/m2/libm2/FORchk.c b/lang/m2/libm2/FORchk.c
new file mode 100644
index 000000000..f911e2955
--- /dev/null
+++ b/lang/m2/libm2/FORchk.c
@@ -0,0 +1,8 @@
+static char m[] = "Warning: FOR-loop control variable was changed in the body";
+_forloopchk(a,b)
+	unsigned a, b;
+{
+	if (a != b) {
+		Traps_Message(m , 0, sizeof(m) - 2, 1);
+	}
+}
diff --git a/lang/m2/libm2/LIST b/lang/m2/libm2/LIST
index f9bd631de..ab3d139b6 100644
--- a/lang/m2/libm2/LIST
+++ b/lang/m2/libm2/LIST
@@ -16,6 +16,7 @@ Semaphores.mod
 random.mod
 Strings.mod
 catch.c
+FORchk.c
 Traps.mod
 Arguments.c
 LtoUset.e