diff --git a/config.c b/config.c
index b6082f597c118d75a9342d1e0bf5788c7a8257ee..c08c66890f0162fe69452927c48d6835178ed12d 100644
--- a/config.c
+++ b/config.c
@@ -661,6 +661,11 @@ int git_config_set_multivar(const char* key, const char* value,
 				goto out_free;
 			}
 			c = tolower(c);
+		} else if (c == '\n') {
+			fprintf(stderr, "invalid key (newline): %s\n", key);
+			free(store.key);
+			ret = 1;
+			goto out_free;
 		}
 		store.key[i] = c;
 	}
diff --git a/t/t1300-repo-config.sh b/t/t1300-repo-config.sh
index 60acdd368bfcb6ccb4698f6fd7533dd25befd9b0..eb7455ba21030252d5e988e2d184d16d63a7ea67 100755
--- a/t/t1300-repo-config.sh
+++ b/t/t1300-repo-config.sh
@@ -418,5 +418,11 @@ EOF
 
 test_expect_success 'quoting' 'cmp .git/config expect'
 
+test_expect_failure 'key with newline' 'git repo-config key.with\\\
+newline 123'
+
+test_expect_success 'value with newline' 'git repo-config key.sub value.with\\\
+newline'
+
 test_done