diff --git a/commit.go b/commit.go
index 758cbda..f4c1a28 100644
--- a/commit.go
+++ b/commit.go
@@ -145,7 +145,7 @@ func (c *Commit) Decode(hash hash.Hash, from io.Reader, size int64) (n int, err
 					c.Committer = ""
 				}
 			default:
-				if strings.HasPrefix(s.Text(), " ") {
+				if strings.HasPrefix(text, " ") && len(c.ExtraHeaders) > 0 {
 					idx := len(c.ExtraHeaders) - 1
 					hdr := c.ExtraHeaders[idx]
 
diff --git a/commit_test.go b/commit_test.go
index 95d6631..804f8cf 100644
--- a/commit_test.go
+++ b/commit_test.go
@@ -455,3 +455,17 @@ func TestCommitEqualReturnsTrueWhenBothCommitsAreNil(t *testing.T) {
 
 	assert.True(t, c1.Equal(c2))
 }
+
+func TestCommitInvalidMultilineNonExtraHeader(t *testing.T) {
+	cc := `tree 2aedfd35087c75d17bdbaf4dd56069d44fc75b71
+parent 75158117eb8efe60453f8c077527ac3530c81e38
+author Jane Doe <jane@example.com> 1503956287 -0400
+committer Jane Doe <jane@example.com> 1503956287 -0400
+ foo bar
+
+initial commit`
+
+	var c Commit
+	_, err := c.Decode(sha1.New(), strings.NewReader(cc), int64(len(cc)))
+	assert.NoError(t, err)
+}