diff --git a/packages/iris-grid/src/IrisGridCacheUtils.test.ts b/packages/iris-grid/src/IrisGridCacheUtils.test.ts
index 4fc045c7f6..cb20f1eff7 100644
--- a/packages/iris-grid/src/IrisGridCacheUtils.test.ts
+++ b/packages/iris-grid/src/IrisGridCacheUtils.test.ts
@@ -51,7 +51,7 @@ const irisGridState = {
   metrics: {
     userColumnWidths: new Map(),
     userRowHeights: new Map(),
-  } as GridMetrics,
+  } as Partial<GridMetrics>,
 } satisfies HydratedIrisGridState;
 
 describe('makeMemoizedGridStateDehydrator', () => {
diff --git a/packages/iris-grid/src/IrisGridUtils.test.ts b/packages/iris-grid/src/IrisGridUtils.test.ts
index b8fe7782a4..8ca16ebcb2 100644
--- a/packages/iris-grid/src/IrisGridUtils.test.ts
+++ b/packages/iris-grid/src/IrisGridUtils.test.ts
@@ -719,7 +719,7 @@ describe('dehydration methods', () => {
         metrics: {
           userColumnWidths: new Map(),
           userRowHeights: new Map(),
-        } as GridMetrics,
+        } as Partial<GridMetrics>,
       }),
     ],
   ])('%s should be serializable', (_label, result) => {
diff --git a/packages/iris-grid/src/IrisGridUtils.ts b/packages/iris-grid/src/IrisGridUtils.ts
index ed325ec339..0296283c70 100644
--- a/packages/iris-grid/src/IrisGridUtils.ts
+++ b/packages/iris-grid/src/IrisGridUtils.ts
@@ -1,4 +1,5 @@
 import {
+  type GridMetrics,
   type GridRange,
   type GridState,
   GridUtils,
@@ -76,8 +77,9 @@ export type HydratedIrisGridState = Pick<
   | 'conditionalFormats'
   | 'columnHeaderGroups'
   | 'partitionConfig'
-  | 'metrics'
->;
+> & {
+  metrics?: Partial<GridMetrics>;
+};
 
 export type DehydratedPendingDataMap<T> = [number, { data: [string, T][] }][];
 
@@ -1192,10 +1194,10 @@ class IrisGridUtils {
       customColumnFormatMap,
       columnAlignmentMap = EMPTY_MAP,
       isFilterBarShown,
-      metrics: { userColumnWidths, userRowHeights } = {
-        userColumnWidths: EMPTY_MAP,
-        userRowHeights: EMPTY_MAP,
-      },
+      metrics: {
+        userColumnWidths = new Map<ModelIndex, number>(),
+        userRowHeights = new Map<ModelIndex, number>(),
+      } = {},
       quickFilters,
       customColumns,
       conditionalFormats = EMPTY_ARRAY,