diff --git a/src/oid.c b/src/oid.c
index e2d16d537..b47fa2c77 100644
--- a/src/oid.c
+++ b/src/oid.c
@@ -34,15 +34,16 @@ static char to_hex[] = "0123456789abcdef";
 int git_oid_fromstrn(git_oid *out, const char *str, size_t length)
 {
 	size_t p;
+	int v;
+
+	if (length < 4)
+		return git__throw(GIT_ENOTOID, "Failed to generate sha1. Given string is too short");
 
 	if (length > GIT_OID_HEXSZ)
 		length = GIT_OID_HEXSZ;
 
-	if (length % 2)
-		length--;
-
-	for (p = 0; p < length; p += 2) {
-		int v = (from_hex[(unsigned char)str[p + 0]] << 4)
+	for (p = 0; p < length - 1; p += 2) {
+		v = (from_hex[(unsigned char)str[p + 0]] << 4)
 				| from_hex[(unsigned char)str[p + 1]];
 
 		if (v < 0)
@@ -51,8 +52,16 @@ int git_oid_fromstrn(git_oid *out, const char *str, size_t length)
 		out->id[p / 2] = (unsigned char)v;
 	}
 
-	for (; p < GIT_OID_HEXSZ; p += 2)
-		out->id[p / 2] = 0x0;
+	if (length % 2) {
+		v = (from_hex[(unsigned char)str[p + 0]] << 4);
+		if (v < 0)
+			return git__throw(GIT_ENOTOID, "Failed to generate sha1. Given string is not a valid sha1 hash");
+
+		out->id[p / 2] = (unsigned char)v;
+		p += 2;
+	}
+
+	memset(out->id + p / 2, 0, (GIT_OID_HEXSZ - p) / 2);
 
 	return GIT_SUCCESS;
 }