diff --git a/lexicons/org/tangled/embed/commit.json b/lexicons/org/tangled/embed/commit.json
index b9184ca4..157edb8b 100644
--- a/lexicons/org/tangled/embed/commit.json
+++ b/lexicons/org/tangled/embed/commit.json
@@ -10,7 +10,7 @@
       ],
       "properties": {
         "repo": { "type": "string", "format": "did" },
-        "commit": { "type": "ref", "ref": "org.tangled.git.object" }
+        "commit": { "type": "ref", "ref": "org.tangled.git.oid" }
       }
     }
   }
diff --git a/lexicons/org/tangled/git/oid.json b/lexicons/org/tangled/git/oid.json
new file mode 100644
index 00000000..6deeaa43
--- /dev/null
+++ b/lexicons/org/tangled/git/oid.json
@@ -0,0 +1,40 @@
+{
+  "lexicon": 1,
+  "id": "org.tangled.git.oid",
+  "description": "Git object-id",
+  "defs": {
+    "main": {
+      "type": "object",
+      "required": ["oid"],
+      "properties": {
+        "oid": {
+          "type": "union",
+          "closed": true,
+          "refs": ["#sha1", "#sha256"]
+        }
+      }
+    },
+    "sha1": {
+      "type": "object",
+      "required": ["hash"],
+      "properties": {
+        "hash": {
+          "type": "string",
+          "minLength": 40,
+          "maxLength": 40
+        }
+      }
+    },
+    "sha256": {
+      "type": "object",
+      "required": ["hash"],
+      "properties": {
+        "hash": {
+          "type": "string",
+          "minLength": 64,
+          "maxLength": 64
+        }
+      }
+    }
+  }
+}
diff --git a/lexicons/org/tangled/git/oid1.json b/lexicons/org/tangled/git/oid1.json
new file mode 100644
index 00000000..be0182be
--- /dev/null
+++ b/lexicons/org/tangled/git/oid1.json
@@ -0,0 +1,18 @@
+{
+  "lexicon": 1,
+  "id": "org.tangled.git.oid1",
+  "description": "Git object-id using SHA-1 hash.",
+  "defs": {
+    "main": {
+      "type": "object",
+      "required": ["hash"],
+      "properties": {
+        "hash": {
+          "type": "string",
+          "minLength": 40,
+          "maxLength": 40
+        }
+      }
+    }
+  }
+}
diff --git a/lexicons/org/tangled/git/oid256.json b/lexicons/org/tangled/git/oid256.json
new file mode 100644
index 00000000..0564b499
--- /dev/null
+++ b/lexicons/org/tangled/git/oid256.json
@@ -0,0 +1,18 @@
+{
+  "lexicon": 1,
+  "id": "org.tangled.git.oid256",
+  "description": "Git object-id using SHA-256 hash.",
+  "defs": {
+    "main": {
+      "type": "object",
+      "required": ["hash"],
+      "properties": {
+        "hash": {
+          "type": "string",
+          "minLength": 64,
+          "maxLength": 64
+        }
+      }
+    }
+  }
+}