diff --git a/.changeset/bright-keys-remember.md b/.changeset/bright-keys-remember.md
new file mode 100644
index 00000000000..3f850346770
--- /dev/null
+++ b/.changeset/bright-keys-remember.md
@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Preserve broad index constraints when generating JSON Schema pattern properties.
diff --git a/packages/effect/src/internal/schema/toJsonSchemaDocument.ts b/packages/effect/src/internal/schema/toJsonSchemaDocument.ts
index 509439970c5..d8d6faba0a5 100644
--- a/packages/effect/src/internal/schema/toJsonSchemaDocument.ts
+++ b/packages/effect/src/internal/schema/toJsonSchemaDocument.ts
@@ -369,6 +369,7 @@ function compileJsonSchema(
         if (representation.propertySignatures.length > 0) out.properties = properties
         if (required.length > 0) out.required = required
         out.additionalProperties = options?.additionalProperties ?? false
+        let hasBroadIndexSignature = false
         const patternProperties: Record<string, JsonSchema.JsonSchema | false> = {}
         for (let index = 0; index < representation.indexSignatures.length; index++) {
           const signature = representation.indexSignatures[index]
@@ -383,6 +384,7 @@ function compileJsonSchema(
             new Set()
           )
           if (patterns.length === 0) {
+            hasBroadIndexSignature = true
             out.additionalProperties = type
           } else {
             for (const pattern of patterns) InternalRecord.assignProperty(patternProperties, pattern, type)
@@ -390,7 +392,7 @@ function compileJsonSchema(
         }
         if (Object.keys(patternProperties).length > 0) {
           out.patternProperties = patternProperties
-          delete out.additionalProperties
+          if (!hasBroadIndexSignature) delete out.additionalProperties
         }
         if (
           typeof out.additionalProperties === "object" &&
diff --git a/packages/effect/test/schema/representation/toJsonSchemaDocument.test.ts b/packages/effect/test/schema/representation/toJsonSchemaDocument.test.ts
index 15d9906e5fc..33940328301 100644
--- a/packages/effect/test/schema/representation/toJsonSchemaDocument.test.ts
+++ b/packages/effect/test/schema/representation/toJsonSchemaDocument.test.ts
@@ -252,6 +252,31 @@ describe("SchemaRepresentation.toJsonSchemaDocument", () => {
         { type: "object" }
       )
     })
+
+    it("retains a broad index constraint alongside patternProperties", () => {
+      const output = compile({
+        _tag: "Objects",
+        propertySignatures: [],
+        indexSignatures: [
+          { parameter: StringRepresentation, type: NumberRepresentation },
+          {
+            parameter: {
+              _tag: "TemplateLiteral",
+              parts: [
+                { _tag: "Literal", literal: "x_", checks: [] },
+                StringRepresentation
+              ],
+              checks: []
+            },
+            type: StringRepresentation
+          }
+        ],
+        checks: []
+      })
+
+      assert.isDefined(output.patternProperties)
+      assert.isDefined(output.additionalProperties)
+    })
   })
 
   describe("unions", () => {