diff --git a/packages/react-resizable-panels/src/utils/computePanelFlexBoxStyle.test.ts b/packages/react-resizable-panels/src/utils/computePanelFlexBoxStyle.test.ts
new file mode 100644
index 000000000..72e2a489e
--- /dev/null
+++ b/packages/react-resizable-panels/src/utils/computePanelFlexBoxStyle.test.ts
@@ -0,0 +1,123 @@
+import { PanelConstraints, PanelData } from "../Panel";
+import { computePanelFlexBoxStyle } from "./computePanelFlexBoxStyle";
+
+describe("computePanelFlexBoxStyle", () => {
+  function createPanelData(constraints: PanelConstraints = {}): PanelData {
+    return {
+      callbacks: {},
+      constraints,
+      id: "fake",
+      idIsFromProps: false,
+      order: undefined,
+    };
+  }
+
+  it("should observe a panel's default size if group layout has not yet been computed", () => {
+    expect(
+      computePanelFlexBoxStyle({
+        defaultSize: 0.1233456789,
+        dragState: null,
+        layout: [],
+        panelData: [
+          createPanelData({
+            defaultSize: 0.1233456789,
+          }),
+          createPanelData(),
+        ],
+        panelIndex: 0,
+        precision: 2,
+      })
+    ).toMatchInlineSnapshot(`
+{
+  "flexBasis": 0,
+  "flexGrow": "0.12",
+  "flexShrink": 1,
+  "overflow": "hidden",
+  "pointerEvents": undefined,
+}
+`);
+  });
+
+  it("should always fill the full width for single-panel groups", () => {
+    expect(
+      computePanelFlexBoxStyle({
+        defaultSize: undefined,
+        dragState: null,
+        layout: [],
+        panelData: [createPanelData()],
+        panelIndex: 0,
+        precision: 2,
+      })
+    ).toMatchInlineSnapshot(`
+{
+  "flexBasis": 0,
+  "flexGrow": "1",
+  "flexShrink": 1,
+  "overflow": "hidden",
+  "pointerEvents": undefined,
+}
+`);
+  });
+
+  it("should round sizes to avoid floating point precision errors", () => {
+    const layout = [0.25435, 0.5758, 0.1698];
+    const panelData = [createPanelData(), createPanelData(), createPanelData()];
+
+    expect(
+      computePanelFlexBoxStyle({
+        defaultSize: undefined,
+        dragState: null,
+        layout,
+        panelData,
+        panelIndex: 0,
+        precision: 2,
+      })
+    ).toMatchInlineSnapshot(`
+{
+  "flexBasis": 0,
+  "flexGrow": "0.25",
+  "flexShrink": 1,
+  "overflow": "hidden",
+  "pointerEvents": undefined,
+}
+`);
+
+    expect(
+      computePanelFlexBoxStyle({
+        defaultSize: undefined,
+        dragState: null,
+        layout,
+        panelData,
+        panelIndex: 1,
+        precision: 2,
+      })
+    ).toMatchInlineSnapshot(`
+{
+  "flexBasis": 0,
+  "flexGrow": "0.58",
+  "flexShrink": 1,
+  "overflow": "hidden",
+  "pointerEvents": undefined,
+}
+`);
+
+    expect(
+      computePanelFlexBoxStyle({
+        defaultSize: undefined,
+        dragState: null,
+        layout,
+        panelData,
+        panelIndex: 2,
+        precision: 2,
+      })
+    ).toMatchInlineSnapshot(`
+{
+  "flexBasis": 0,
+  "flexGrow": "0.17",
+  "flexShrink": 1,
+  "overflow": "hidden",
+  "pointerEvents": undefined,
+}
+`);
+  });
+});
diff --git a/packages/react-resizable-panels/src/utils/computePanelFlexBoxStyle.ts b/packages/react-resizable-panels/src/utils/computePanelFlexBoxStyle.ts
index c48e2307c..2fba40b1d 100644
--- a/packages/react-resizable-panels/src/utils/computePanelFlexBoxStyle.ts
+++ b/packages/react-resizable-panels/src/utils/computePanelFlexBoxStyle.ts
@@ -26,7 +26,8 @@ export function computePanelFlexBoxStyle({
   if (size == null) {
     // Initial render (before panels have registered themselves)
     // In order to support server rendering, fall back to default size if provided
-    flexGrow = defaultSize ?? "1";
+    flexGrow =
+      defaultSize != undefined ? defaultSize.toPrecision(precision) : "1";
   } else if (panelData.length === 1) {
     // Special case: Single panel group should always fill full width/height
     flexGrow = "1";