diff --git a/crates/language_model/src/tool_schema.rs b/crates/language_model/src/tool_schema.rs
index 6fbb3761b43ea04924aaa23373920c41a14c74e3..69afcd1f288064748e3c953a27003361ed5115b0 100644
--- a/crates/language_model/src/tool_schema.rs
+++ b/crates/language_model/src/tool_schema.rs
@@ -105,9 +105,12 @@ fn adapt_to_json_schema_subset(json: &mut Value) -> Result<()> {
             );
         }
 
-        const KEYS_TO_REMOVE: [(&str, fn(&Value) -> bool); 5] = [
+        const KEYS_TO_REMOVE: [(&str, fn(&Value) -> bool); 6] = [
             ("format", |value| value.is_string()),
-            ("additionalProperties", |value| value.is_boolean()),
+            // Gemini doesn't support `additionalProperties` in any form (boolean or schema object)
+            ("additionalProperties", |_| true),
+            // Gemini doesn't support `propertyNames`
+            ("propertyNames", |_| true),
             ("exclusiveMinimum", |value| value.is_number()),
             ("exclusiveMaximum", |value| value.is_number()),
             ("optional", |value| value.is_boolean()),
@@ -234,6 +237,28 @@ mod tests {
                 "format": {},
             })
         );
+
+        // additionalProperties as an object schema is also unsupported by Gemini
+        let mut json = json!({
+            "type": "object",
+            "properties": {
+                "name": { "type": "string" }
+            },
+            "additionalProperties": { "type": "string" },
+            "propertyNames": { "pattern": "^[A-Za-z]+$" }
+        });
+
+        adapt_to_json_schema_subset(&mut json).unwrap();
+
+        assert_eq!(
+            json,
+            json!({
+                "type": "object",
+                "properties": {
+                    "name": { "type": "string" }
+                }
+            })
+        );
     }
 
     #[test]