diff --git a/Documentation/merge-options.txt b/Documentation/merge-options.txt
index 61876dbc335e240b8842aba3dd4e3fd8a54e574a..79a00d2a4abd6f7191f2639185e199fa85f6289b 100644
--- a/Documentation/merge-options.txt
+++ b/Documentation/merge-options.txt
@@ -102,6 +102,8 @@ merge.
 +
 With --no-squash perform the merge and commit the result. This
 option can be used to override --squash.
++
+With --squash, --commit is not allowed, and will fail.
 
 -s <strategy>::
 --strategy=<strategy>::
diff --git a/builtin/merge.c b/builtin/merge.c
index e96f72af8044769df6b4ef42f0525b572b0c39e2..57c2a24f6d82fc7cedcc86979db6ff1a8fa6bc50 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -58,7 +58,7 @@ static const char * const builtin_merge_usage[] = {
 };
 
 static int show_diffstat = 1, shortlog_len = -1, squash;
-static int option_commit = 1;
+static int option_commit = -1;
 static int option_edit = -1;
 static int allow_trivial = 1, have_message, verify_signatures;
 static int overwrite_ignore = 1;
@@ -1339,9 +1339,19 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 	if (squash) {
 		if (fast_forward == FF_NO)
 			die(_("You cannot combine --squash with --no-ff."));
+		if (option_commit > 0)
+			die(_("You cannot combine --squash with --commit."));
+		/*
+		 * squash can now silently disable option_commit - this is not
+		 * a problem as it is only overriding the default, not a user
+		 * supplied option.
+		 */
 		option_commit = 0;
 	}
 
+	if (option_commit < 0)
+		option_commit = 1;
+
 	if (!argc) {
 		if (default_to_upstream)
 			argc = setup_with_upstream(&argv);
diff --git a/t/t7600-merge.sh b/t/t7600-merge.sh
index 7f9c68cbe75a688357e6c71486c3897861421681..4ec5d9ec790a0d54f4883fc118b5df25c94f43f4 100755
--- a/t/t7600-merge.sh
+++ b/t/t7600-merge.sh
@@ -570,6 +570,12 @@ test_expect_success 'combining --squash and --no-ff is refused' '
 	test_must_fail git merge --no-ff --squash c1
 '
 
+test_expect_success 'combining --squash and --commit is refused' '
+	git reset --hard c0 &&
+	test_must_fail git merge --squash --commit c1 &&
+	test_must_fail git merge --commit --squash c1
+'
+
 test_expect_success 'option --ff-only overwrites --no-ff' '
 	git merge --no-ff --ff-only c1 &&
 	test_must_fail git merge --no-ff --ff-only c2