diff --git a/main.c b/main.c
index 25a628ba..c06f56af 100644
--- a/main.c
+++ b/main.c
@@ -1165,6 +1165,15 @@ arg_assign(char *arg, bool initing)
 				fatal(_("cannot use function `%s' as variable name"), arg);
 		}
 
+		/* Assignment operands in which the right-hand side
+		 * contains a literal newline are not permitted.
+		 * Specified in IEEE Std 1003.1, implemented in BWK awk.
+		 */
+		if (do_traditional)
+			for (cp2 = cp; *cp2; cp2++)
+				if (*cp2 == '\n')
+					fatal(_("newline in string `%s' not permitted in compatibility mode"), cp);
+
 		/*
 		 * BWK awk expands escapes inside assignments.
 		 * This makes sense, so we do it too.