diff --git a/packages/excalidraw/components/ConvertElementTypePopup.tsx b/packages/excalidraw/components/ConvertElementTypePopup.tsx
index 48da586b05..5f02212012 100644
--- a/packages/excalidraw/components/ConvertElementTypePopup.tsx
+++ b/packages/excalidraw/components/ConvertElementTypePopup.tsx
@@ -831,14 +831,13 @@ const convertElementType = <
       newElement({
         ...element,
         type: targetType,
-        roundness:
-          targetType === "diamond" && element.roundness
-            ? {
-                type: isUsingAdaptiveRadius(targetType)
-                  ? ROUNDNESS.ADAPTIVE_RADIUS
-                  : ROUNDNESS.PROPORTIONAL_RADIUS,
-              }
-            : element.roundness,
+        roundness: element.roundness
+          ? {
+              type: isUsingAdaptiveRadius(targetType)
+                ? ROUNDNESS.ADAPTIVE_RADIUS
+                : ROUNDNESS.PROPORTIONAL_RADIUS,
+            }
+          : element.roundness,
       }),
     ) as typeof element;
 
diff --git a/packages/excalidraw/tests/convertElementType.test.tsx b/packages/excalidraw/tests/convertElementType.test.tsx
new file mode 100644
index 0000000000..c55e9df66e
--- /dev/null
+++ b/packages/excalidraw/tests/convertElementType.test.tsx
@@ -0,0 +1,46 @@
+import { ROUNDNESS } from "@excalidraw/common";
+
+import { convertElementTypes } from "../components/ConvertElementTypePopup";
+import { Excalidraw } from "../index";
+
+import { API } from "./helpers/api";
+import { act, render } from "./test-utils";
+
+const { h } = window;
+
+describe("convert element type", () => {
+  beforeEach(async () => {
+    await render(<Excalidraw handleKeyboardGlobally={true} />);
+  });
+
+  // #9662
+  it("recalculates roundness type when switching between generic shapes", () => {
+    const rectangle = API.createElement({
+      type: "rectangle",
+      roundness: { type: ROUNDNESS.ADAPTIVE_RADIUS }, // Dooesn't matter as long as it is set
+    });
+
+    API.setElements([rectangle]);
+    API.setSelectedElements([rectangle]);
+
+    act(() => {
+      convertElementTypes(h.app, {
+        conversionType: "generic",
+        nextType: "diamond",
+      });
+    });
+
+    expect(h.elements[0].type).toBe("diamond");
+    expect(h.elements[0].roundness?.type).toBe(ROUNDNESS.PROPORTIONAL_RADIUS);
+
+    act(() => {
+      convertElementTypes(h.app, {
+        conversionType: "generic",
+        nextType: "rectangle",
+      });
+    });
+
+    expect(h.elements[0].type).toBe("rectangle");
+    expect(h.elements[0].roundness?.type).toBe(ROUNDNESS.ADAPTIVE_RADIUS);
+  });
+});
diff --git a/packages/excalidraw/tests/data/__snapshots__/restore.test.ts.snap b/packages/excalidraw/tests/data/__snapshots__/restore.test.ts.snap
index e3c0581522..b1d267c3ba 100644
--- a/packages/excalidraw/tests/data/__snapshots__/restore.test.ts.snap
+++ b/packages/excalidraw/tests/data/__snapshots__/restore.test.ts.snap
@@ -154,7 +154,7 @@ exports[`restoreElements > should restore correctly with rectangle, ellipse and
   "opacity": 10,
   "roughness": 2,
   "roundness": {
-    "type": 3,
+    "type": 2,
   },
   "seed": Any<Number>,
   "strokeColor": "red",
@@ -192,7 +192,7 @@ exports[`restoreElements > should restore correctly with rectangle, ellipse and
   "opacity": 10,
   "roughness": 2,
   "roundness": {
-    "type": 3,
+    "type": 2,
   },
   "seed": Any<Number>,
   "strokeColor": "red",
diff --git a/packages/excalidraw/tests/helpers/api.ts b/packages/excalidraw/tests/helpers/api.ts
index 95d8d34084..5628228639 100644
--- a/packages/excalidraw/tests/helpers/api.ts
+++ b/packages/excalidraw/tests/helpers/api.ts
@@ -19,8 +19,7 @@ import {
   newTextElement,
 } from "@excalidraw/element";
 
-import { isLinearElementType } from "@excalidraw/element";
-import { getSelectedElements } from "@excalidraw/element";
+import { isUsingAdaptiveRadius, getSelectedElements } from "@excalidraw/element";
 import { selectGroupsForSelectedElements } from "@excalidraw/element";
 
 import { FONT_SIZES } from "@excalidraw/common";
@@ -267,9 +266,9 @@ export class API {
           : rest.roundness
       )
         ? {
-            type: isLinearElementType(type)
-              ? ROUNDNESS.PROPORTIONAL_RADIUS
-              : ROUNDNESS.ADAPTIVE_RADIUS,
+            type: isUsingAdaptiveRadius(type)
+                    ? ROUNDNESS.ADAPTIVE_RADIUS
+                    : ROUNDNESS.PROPORTIONAL_RADIUS,
           }
         : null,
       roughness: rest.roughness ?? appState.currentItemRoughness,