diff --git a/branch.c b/branch.c
index 7ff3f2049..713ceda36 100644
--- a/branch.c
+++ b/branch.c
@@ -49,7 +49,13 @@ static int should_setup_rebase(const char *origin)
 	return 0;
 }
 
-void install_branch_config(int flag, const char *local, const char *origin, const char *remote)
+static const char tracking_advice[] =
+N_("\n"
+"After fixing the error cause you may try to fix up\n"
+"the remote tracking information by invoking\n"
+"\"git branch --set-upstream-to=%s%s%s\".");
+
+int install_branch_config(int flag, const char *local, const char *origin, const char *remote)
 {
 	const char *shortname = NULL;
 	struct strbuf key = STRBUF_INIT;
@@ -60,20 +66,23 @@ void install_branch_config(int flag, const char *local, const char *origin, cons
 	    && !origin) {
 		warning(_("Not setting branch %s as its own upstream."),
 			local);
-		return;
+		return 0;
 	}
 
 	strbuf_addf(&key, "branch.%s.remote", local);
-	git_config_set(key.buf, origin ? origin : ".");
+	if (git_config_set(key.buf, origin ? origin : ".") < 0)
+		goto out_err;
 
 	strbuf_reset(&key);
 	strbuf_addf(&key, "branch.%s.merge", local);
-	git_config_set(key.buf, remote);
+	if (git_config_set(key.buf, remote) < 0)
+		goto out_err;
 
 	if (rebasing) {
 		strbuf_reset(&key);
 		strbuf_addf(&key, "branch.%s.rebase", local);
-		git_config_set(key.buf, "true");
+		if (git_config_set(key.buf, "true") < 0)
+			goto out_err;
 	}
 	strbuf_release(&key);
 
@@ -102,6 +111,19 @@ void install_branch_config(int flag, const char *local, const char *origin, cons
 					  local, remote);
 		}
 	}
+
+	return 0;
+
+out_err:
+	strbuf_release(&key);
+	error(_("Unable to write upstream branch configuration"));
+
+	advise(_(tracking_advice),
+	       origin ? origin : "",
+	       origin ? "/" : "",
+	       shortname ? shortname : remote);
+
+	return -1;
 }
 
 /*
@@ -109,8 +131,8 @@ void install_branch_config(int flag, const char *local, const char *origin, cons
  * to infer the settings for branch.<new_ref>.{remote,merge} from the
  * config.
  */
-static int setup_tracking(const char *new_ref, const char *orig_ref,
-			  enum branch_track track, int quiet)
+static void setup_tracking(const char *new_ref, const char *orig_ref,
+			   enum branch_track track, int quiet)
 {
 	struct tracking tracking;
 	int config_flags = quiet ? 0 : BRANCH_CONFIG_VERBOSE;
@@ -118,7 +140,7 @@ static int setup_tracking(const char *new_ref, const char *orig_ref,
 	memset(&tracking, 0, sizeof(tracking));
 	tracking.spec.dst = (char *)orig_ref;
 	if (for_each_remote(find_tracked_branch, &tracking))
-		return 1;
+		return;
 
 	if (!tracking.matches)
 		switch (track) {
@@ -127,18 +149,18 @@ static int setup_tracking(const char *new_ref, const char *orig_ref,
 		case BRANCH_TRACK_OVERRIDE:
 			break;
 		default:
-			return 1;
+			return;
 		}
 
 	if (tracking.matches > 1)
-		return error(_("Not tracking: ambiguous information for ref %s"),
-				orig_ref);
+		die(_("Not tracking: ambiguous information for ref %s"),
+		    orig_ref);
 
-	install_branch_config(config_flags, new_ref, tracking.remote,
-			      tracking.src ? tracking.src : orig_ref);
+	if (install_branch_config(config_flags, new_ref, tracking.remote,
+			      tracking.src ? tracking.src : orig_ref) < 0)
+		exit(-1);
 
 	free(tracking.src);
-	return 0;
 }
 
 int read_branch_desc(struct strbuf *buf, const char *branch_name)
diff --git a/branch.h b/branch.h
index 58aa45fe7..78ad4387c 100644
--- a/branch.h
+++ b/branch.h
@@ -43,9 +43,10 @@ void remove_branch_state(void);
 /*
  * Configure local branch "local" as downstream to branch "remote"
  * from remote "origin".  Used by git branch --set-upstream.
+ * Returns 0 on success.
  */
 #define BRANCH_CONFIG_VERBOSE 01
-extern void install_branch_config(int flag, const char *local, const char *origin, const char *remote);
+extern int install_branch_config(int flag, const char *local, const char *origin, const char *remote);
 
 /*
  * Read branch description
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index cdaf6f64e..dd776b355 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -446,6 +446,13 @@ test_expect_success '--set-upstream-to fails on a non-ref' '
 	test_must_fail git branch --set-upstream-to HEAD^{}
 '
 
+test_expect_success '--set-upstream-to fails on locked config' '
+	test_when_finished "rm -f .git/config.lock" &&
+	>.git/config.lock &&
+	git branch locked &&
+	test_must_fail git branch --set-upstream-to locked
+'
+
 test_expect_success 'use --set-upstream-to modify HEAD' '
 	test_config branch.master.remote foo &&
 	test_config branch.master.merge foo &&
@@ -579,7 +586,7 @@ test_expect_success 'avoid ambiguous track' '
 	git config remote.ambi1.fetch refs/heads/lalala:refs/heads/master &&
 	git config remote.ambi2.url lilili &&
 	git config remote.ambi2.fetch refs/heads/lilili:refs/heads/master &&
-	git branch all1 master &&
+	test_must_fail git branch all1 master &&
 	test -z "$(git config branch.all1.merge)"
 '