diff --git a/release/UNIVERSAL_SpineViewer/viewer/spine.html b/release/UNIVERSAL_SpineViewer/viewer/spine.html
index 055af0c..31e2bd8 100644
--- a/release/UNIVERSAL_SpineViewer/viewer/spine.html
+++ b/release/UNIVERSAL_SpineViewer/viewer/spine.html
@@ -491,11 +491,11 @@
 	// baseFitScale 为自动适配用的基准缩放；panX/panY/zoom 为用户平移/缩放叠加。
 	// fitScale = baseFitScale * zoom；fitCx/fitCy 是骨骼包围盒中心（世界坐标）。
 	let fitScale = 1, fitCx = 0, fitCy = 0;
-	function captureStableFitBounds() {
-		const bounds = getBounds(skeleton);
+	function captureStableFitBounds(bounds = getBounds(skeleton)) {
 		stableFitBounds = bounds && bounds.width > 0 && bounds.height > 0
 			? { x: bounds.x, y: bounds.y, width: bounds.width, height: bounds.height }
 			: null;
+		return stableFitBounds !== null;
 	}
 
 	function fitToCanvas() {
@@ -504,7 +504,7 @@
 		const bounds = stableFitBounds;
 		const cw = canvas.clientWidth, ch = canvas.clientHeight;
 		if (!bounds || bounds.width <= 0 || bounds.height <= 0) {
-			baseFitScale = 1; baseFitCx = 0; baseFitCy = 0; fitScale = 1; fitCx = 0; fitCy = 0; return;
+			baseFitScale = 1; baseFitCx = 0; baseFitCy = 0; fitScale = zoom; fitCx = 0; fitCy = 0; return;
 		}
 		const pad = 0.1;
 		const sx = (cw * (1 - pad * 2)) / bounds.width;
@@ -1440,7 +1440,7 @@
 		}
 	}
 
-	function setAnimationByName(name, index) {
+	async function setAnimationByName(name, index) {
 		if (!state) return;
 		const anim = findAnimByName(name);
 		if (!anim) return;
@@ -1452,6 +1452,11 @@
 		state.update(0);
 		state.apply(skeleton);
 		updateWorld(skeleton);
+		if (!stableFitBounds) {
+			const geometryBounds = getBounds(skeleton);
+			const bounds = await measureVisibleBounds(skeleton, geometryBounds, 1, () => {}) || geometryBounds;
+			if (currentAnim === resolvedIndex && captureStableFitBounds(bounds)) fitToCanvas();
+		}
 		draw();
 	}
 
diff --git a/tests/setup-pose-zoom.test.js b/tests/setup-pose-zoom.test.js
index 1f1e9fe..77d63ae 100644
--- a/tests/setup-pose-zoom.test.js
+++ b/tests/setup-pose-zoom.test.js
@@ -31,9 +31,11 @@ for (const root of roots) {
 	const fit = functionBody(script, 'fitToCanvas', 'draw');
 	assert.match(fit, /const bounds = stableFitBounds;/);
 	assert.doesNotMatch(fit, /getBounds\(/, 'wheel/resize fitting must not sample an animated frame');
+	assert.match(fit, /fitScale = zoom;/, 'wheel zoom must still work before a drawable stable bound exists');
 
 	const capture = functionBody(script, 'captureStableFitBounds', 'fitToCanvas');
 	assert.match(capture, /getBounds\(skeleton\)/);
+	assert.match(script, /async function setAnimationByName[\s\S]*if \(!stableFitBounds\)[\s\S]*measureVisibleBounds\(skeleton, geometryBounds, 1[\s\S]*captureStableFitBounds\(bounds\)/);
 	assert.match(css, /#status \{\s*position: absolute; left: 50%;[^}]*transform: translateX\(-50%\)/, 'status notice must be horizontally centered');
 
 	const manifest = JSON.parse(fs.readFileSync(path.join(root, 'manifest.json'), 'utf8'));
diff --git a/viewer/spine.html b/viewer/spine.html
index 055af0c..31e2bd8 100644
--- a/viewer/spine.html
+++ b/viewer/spine.html
@@ -491,11 +491,11 @@
 	// baseFitScale 为自动适配用的基准缩放；panX/panY/zoom 为用户平移/缩放叠加。
 	// fitScale = baseFitScale * zoom；fitCx/fitCy 是骨骼包围盒中心（世界坐标）。
 	let fitScale = 1, fitCx = 0, fitCy = 0;
-	function captureStableFitBounds() {
-		const bounds = getBounds(skeleton);
+	function captureStableFitBounds(bounds = getBounds(skeleton)) {
 		stableFitBounds = bounds && bounds.width > 0 && bounds.height > 0
 			? { x: bounds.x, y: bounds.y, width: bounds.width, height: bounds.height }
 			: null;
+		return stableFitBounds !== null;
 	}
 
 	function fitToCanvas() {
@@ -504,7 +504,7 @@
 		const bounds = stableFitBounds;
 		const cw = canvas.clientWidth, ch = canvas.clientHeight;
 		if (!bounds || bounds.width <= 0 || bounds.height <= 0) {
-			baseFitScale = 1; baseFitCx = 0; baseFitCy = 0; fitScale = 1; fitCx = 0; fitCy = 0; return;
+			baseFitScale = 1; baseFitCx = 0; baseFitCy = 0; fitScale = zoom; fitCx = 0; fitCy = 0; return;
 		}
 		const pad = 0.1;
 		const sx = (cw * (1 - pad * 2)) / bounds.width;
@@ -1440,7 +1440,7 @@
 		}
 	}
 
-	function setAnimationByName(name, index) {
+	async function setAnimationByName(name, index) {
 		if (!state) return;
 		const anim = findAnimByName(name);
 		if (!anim) return;
@@ -1452,6 +1452,11 @@
 		state.update(0);
 		state.apply(skeleton);
 		updateWorld(skeleton);
+		if (!stableFitBounds) {
+			const geometryBounds = getBounds(skeleton);
+			const bounds = await measureVisibleBounds(skeleton, geometryBounds, 1, () => {}) || geometryBounds;
+			if (currentAnim === resolvedIndex && captureStableFitBounds(bounds)) fitToCanvas();
+		}
 		draw();
 	}