diff --git a/src/core/pattern.js b/src/core/pattern.js
index 68042e58ddfd5..6059fdfcf8f4a 100644
--- a/src/core/pattern.js
+++ b/src/core/pattern.js
@@ -163,19 +163,6 @@ class RadialAxialShading extends BaseShading {
       [extendStart, extendEnd] = extendArr;
     }
 
-    if (
-      this.shadingType === ShadingType.RADIAL &&
-      (!extendStart || !extendEnd)
-    ) {
-      // Radial gradient only currently works if either circle is fully within
-      // the other circle.
-      const [x1, y1, r1, x2, y2, r2] = this.coordsArr;
-      const distance = Math.hypot(x1 - x2, y1 - y2);
-      if (r1 <= r2 + distance && r2 <= r1 + distance) {
-        warn("Unsupported radial gradient.");
-      }
-    }
-
     this.extendStart = extendStart;
     this.extendEnd = extendEnd;
 
diff --git a/src/display/pattern_helper.js b/src/display/pattern_helper.js
index d460de365637e..5a8da30a57b64 100644
--- a/src/display/pattern_helper.js
+++ b/src/display/pattern_helper.js
@@ -83,6 +83,23 @@ class RadialAxialShadingPattern extends BaseShadingPattern {
     return this._type === "radial";
   }
 
+  // Returns true when the smaller circle's center (p0 when r0 ≤ r1) lies
+  // outside the larger circle. In that case the canvas radial gradient picks
+  // t > 1 solutions for points inside the outer circle and maps them to the
+  // transparent stop we append for extendEnd=false, making the gradient
+  // invisible. A two-pass draw (reversed first, normal on top) fixes this
+  // (see #20851).
+  _isCircleCenterOutside() {
+    if (!this.isRadial() || this._r0 > this._r1) {
+      return false;
+    }
+    const dist = Math.hypot(
+      this._p0[0] - this._p1[0],
+      this._p0[1] - this._p1[1]
+    );
+    return dist > this._r1;
+  }
+
   _createGradient(ctx, transform = null) {
     let grad;
     let firstPoint = this._p0;
@@ -125,6 +142,41 @@ class RadialAxialShadingPattern extends BaseShadingPattern {
     return grad;
   }
 
+  _createReversedGradient(ctx, transform = null) {
+    // Swapped circles: (p1, r1) → (p0, r0), with color stops reversed.
+    let firstPoint = this._p1;
+    let secondPoint = this._p0;
+    if (transform) {
+      firstPoint = firstPoint.slice();
+      secondPoint = secondPoint.slice();
+      Util.applyTransform(firstPoint, transform);
+      Util.applyTransform(secondPoint, transform);
+    }
+    let r0 = this._r1;
+    let r1 = this._r0;
+    if (transform) {
+      const scale = new Float32Array(2);
+      Util.singularValueDecompose2dScale(transform, scale);
+      r0 *= scale[0];
+      r1 *= scale[0];
+    }
+    const grad = ctx.createRadialGradient(
+      firstPoint[0],
+      firstPoint[1],
+      r0,
+      secondPoint[0],
+      secondPoint[1],
+      r1
+    );
+    const reversedStops = this._colorStops
+      .map(([t, c]) => [1 - t, c])
+      .reverse();
+    for (const [t, c] of reversedStops) {
+      grad.addColorStop(t, c);
+    }
+    return grad;
+  }
+
   getPattern(ctx, owner, inverse, pathType) {
     let pattern;
     if (pathType === PathType.STROKE || pathType === PathType.FILL) {
@@ -193,6 +245,10 @@ class RadialAxialShadingPattern extends BaseShadingPattern {
       }
       applyBoundingBox(tmpCtx, this._bbox);
 
+      if (this._isCircleCenterOutside()) {
+        tmpCtx.fillStyle = this._createReversedGradient(tmpCtx);
+        tmpCtx.fill();
+      }
       tmpCtx.fillStyle = this._createGradient(tmpCtx);
       tmpCtx.fill();
 
@@ -203,6 +259,15 @@ class RadialAxialShadingPattern extends BaseShadingPattern {
       // Shading fills are applied relative to the current matrix which is also
       // how canvas gradients work, so there's no need to do anything special
       // here.
+      if (this._isCircleCenterOutside()) {
+        // Draw the reversed gradient first so the normal gradient can
+        // correctly overlay it (see _isCircleCenterOutside for details).
+        ctx.save();
+        applyBoundingBox(ctx, this._bbox);
+        ctx.fillStyle = this._createReversedGradient(ctx);
+        ctx.fillRect(-1e10, -1e10, 2e10, 2e10);
+        ctx.restore();
+      }
       applyBoundingBox(ctx, this._bbox);
       pattern = this._createGradient(ctx);
     }
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index 3f85ddfda2aa6..8e4b0a508fc9f 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -883,3 +883,4 @@
 !nested_outline.pdf
 !form_two_pages.pdf
 !outlines_se.pdf
+!radial_gradients.pdf
diff --git a/test/pdfs/radial_gradients.pdf b/test/pdfs/radial_gradients.pdf
new file mode 100644
index 0000000000000..edbf57481f7e3
Binary files /dev/null and b/test/pdfs/radial_gradients.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index 9060f2481f8b5..96245b451bed9 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -13079,7 +13079,11 @@
     "rounds": 1,
     "type": "extract",
     "includePages": [0, 2, 12],
-    "pageMapping": { "1": 1, "3": 2, "13": 3 }
+    "pageMapping": {
+      "1": 1,
+      "3": 2,
+      "13": 3
+    }
   },
   {
     "id": "bug900822-encrypted-extract_0",
@@ -13088,7 +13092,9 @@
     "rounds": 1,
     "type": "extract",
     "includePages": [0],
-    "pageMapping": { "1": 1 }
+    "pageMapping": {
+      "1": 1
+    }
   },
   {
     "id": "xfa_bug1998843",
@@ -13985,5 +13991,12 @@
     "md5": "7072f6763bf2f0d6df14d5fc86962c5a",
     "rounds": 1,
     "type": "eq"
+  },
+  {
+    "id": "radial_gradients",
+    "file": "pdfs/radial_gradients.pdf",
+    "md5": "80e8bed66b83928698f008c33de47edd",
+    "rounds": 1,
+    "type": "eq"
   }
 ]