diff --git a/CHANGELOG.md b/CHANGELOG.md
index 710d4a14f..74f72f10e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Detect utilities when containing capital letters followed by numbers ([#19465](https://github.com/tailwindlabs/tailwindcss/pull/19465))
 - Fix class extraction for Rails' strict locals ([#19525](https://github.com/tailwindlabs/tailwindcss/pull/19525))
 - Align `@utility` name validation with Oxide scanner rules ([#19524](https://github.com/tailwindlabs/tailwindcss/pull/19524))
+- Fix infinite loop when using `@variant` inside `@custom-variant` ([#19633](https://github.com/tailwindlabs/tailwindcss/pull/19633))
 
 ### Deprecated
 
diff --git a/packages/tailwindcss/src/index.test.ts b/packages/tailwindcss/src/index.test.ts
index 94b17714e..5182cdd14 100644
--- a/packages/tailwindcss/src/index.test.ts
+++ b/packages/tailwindcss/src/index.test.ts
@@ -4558,6 +4558,97 @@ describe('@custom-variant', () => {
     `)
   })
 
+  // https://github.com/tailwindlabs/tailwindcss/issues/19618
+  test('@custom-variant can use a @variant that eventually uses another @custom-variant', async () => {
+    expect(
+      await compileCss(
+        css`
+          @custom-variant a {
+            @slot;
+          }
+
+          @custom-variant b {
+            @variant a {
+              @slot;
+            }
+          }
+
+          @tailwind utilities;
+        `,
+        ['a:flex', 'b:flex', 'a:b:flex', 'b:a:flex'],
+      ),
+    ).toMatchInlineSnapshot(`
+      ".a\\:flex, .b\\:flex, .a\\:b\\:flex, .b\\:a\\:flex {
+        display: flex;
+      }"
+    `)
+  })
+
+  test('@custom-variant can use a @variant that eventually uses another @custom-variant (2)', async () => {
+    expect(
+      await compileCss(
+        css`
+          @custom-variant a {
+            .a {
+              @slot;
+            }
+          }
+
+          @custom-variant b {
+            .b {
+              @variant a {
+                .a-inside-b {
+                  @slot;
+                }
+              }
+            }
+          }
+
+          @tailwind utilities;
+        `,
+        ['a:flex', 'b:flex', 'a:b:flex', 'b:a:flex'],
+      ),
+    ).toMatchInlineSnapshot(`
+      ".a\\:flex .a, .b\\:flex .b .a .a-inside-b, .a\\:b\\:flex .a .b .a .a-inside-b, .b\\:a\\:flex .b .a .a-inside-b .a {
+        display: flex;
+      }"
+    `)
+  })
+
+  // https://github.com/tailwindlabs/tailwindcss/issues/19618#issuecomment-3830775912
+  test('@custom-variant can use existing @slot @variants', async () => {
+    expect(
+      await compileCss(
+        css`
+          @custom-variant hocus {
+            @variant hover {
+              @variant focus {
+                @slot;
+              }
+            }
+          }
+
+          @custom-variant hover {
+            &:hover {
+              @slot;
+            }
+
+            &[data-hover] {
+              @slot;
+            }
+          }
+
+          @tailwind utilities;
+        `,
+        ['hocus:flex'],
+      ),
+    ).toMatchInlineSnapshot(`
+      ".hocus\\:flex:hover:focus, .hocus\\:flex[data-hover]:focus {
+        display: flex;
+      }"
+    `)
+  })
+
   test('@custom-variant setup that results in a circular dependency error can be solved', async () => {
     expect(
       await compileCss(
diff --git a/packages/tailwindcss/src/variants.ts b/packages/tailwindcss/src/variants.ts
index 82a2b8592..0b4bcb0c5 100644
--- a/packages/tailwindcss/src/variants.ts
+++ b/packages/tailwindcss/src/variants.ts
@@ -1196,7 +1196,7 @@ export function substituteAtSlot(ast: AstNode[], nodes: AstNode[]) {
   walk(ast, (node) => {
     // Replace `@slot` with rule nodes
     if (node.kind === 'at-rule' && node.name === '@slot') {
-      return WalkAction.Replace(nodes)
+      return WalkAction.ReplaceSkip(nodes)
     }
 
     // Wrap `@keyframes` and `@property` in `AtRoot` nodes