diff --git a/boot/bootflow.c b/boot/bootflow.c
index be543c8588..6922e7e0c4 100644
--- a/boot/bootflow.c
+++ b/boot/bootflow.c
@@ -752,7 +752,7 @@ int cmdline_set_arg(char *buf, int maxlen, const char *cmdline,
 					in_quote = false;
 				continue;
 			}
-			if (*p == '=') {
+			if (*p == '=' && !arg_end) {
 				arg_end = p;
 				val = p + 1;
 			} else if (*p == '"') {
@@ -788,7 +788,8 @@ int cmdline_set_arg(char *buf, int maxlen, const char *cmdline,
 		}
 
 		/* if this is the target arg, update it */
-		if (!strncmp(from, set_arg, arg_end - from)) {
+		if (arg_end - from == set_arg_len &&
+		    !strncmp(from, set_arg, set_arg_len)) {
 			if (!buf) {
 				bool has_quote = val_end[-1] == '"';
 
diff --git a/test/boot/bootflow.c b/test/boot/bootflow.c
index f5b2059140..f640db8a24 100644
--- a/test/boot/bootflow.c
+++ b/test/boot/bootflow.c
@@ -973,6 +973,26 @@ static int bootflow_cmdline(struct unit_test_state *uts)
 }
 BOOTSTD_TEST(bootflow_cmdline, 0);
 
+/* test a few special changes to a long command line */
+static int bootflow_cmdline_special(struct unit_test_state *uts)
+{
+	char buf[500];
+	int pos;
+
+	/*
+	 * check handling of an argument which has an embedded '=', as well as
+	 * handling of a argument which partially matches ("ro" and "root")
+	 */
+	ut_asserteq(32, cmdline_set_arg(
+		buf, sizeof(buf),
+		"loglevel=7 root=PARTUUID=d68352e3 rootwait ro noinitrd",
+		"root", NULL, &pos));
+	ut_asserteq_str("loglevel=7 rootwait ro noinitrd", buf);
+
+	return 0;
+}
+BOOTSTD_TEST(bootflow_cmdline_special, 0);
+
 /* Test ChromiumOS bootmeth */
 static int bootflow_cros(struct unit_test_state *uts)
 {