diff --git a/modules/openapi-generator/src/main/resources/python-fastapi/endpoint_argument_definition.mustache b/modules/openapi-generator/src/main/resources/python-fastapi/endpoint_argument_definition.mustache
index c8887fb64f4e..706b648e0151 100644
--- a/modules/openapi-generator/src/main/resources/python-fastapi/endpoint_argument_definition.mustache
+++ b/modules/openapi-generator/src/main/resources/python-fastapi/endpoint_argument_definition.mustache
@@ -1 +1 @@
-{{#isPathParam}}{{baseName}}{{/isPathParam}}{{^isPathParam}}{{paramName}}{{/isPathParam}}: {{>param_type}} = {{#isPathParam}}Path{{/isPathParam}}{{#isHeaderParam}}Header{{/isHeaderParam}}{{#isFormParam}}Form{{/isFormParam}}{{#isQueryParam}}Query{{/isQueryParam}}{{#isCookieParam}}Cookie{{/isCookieParam}}{{#isBodyParam}}Body{{/isBodyParam}}({{&defaultValue}}{{^defaultValue}}{{#isPathParam}}...{{/isPathParam}}{{^isPathParam}}None{{/isPathParam}}{{/defaultValue}}, description="{{description}}"{{#isQueryParam}}, alias="{{baseName}}"{{/isQueryParam}}{{#isLong}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isLong}}{{#isInteger}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isInteger}}{{#pattern}}, regex=r"{{.}}"{{/pattern}}{{#minLength}}, min_length={{.}}{{/minLength}}{{#maxLength}}, max_length={{.}}{{/maxLength}})
\ No newline at end of file
+{{#isPathParam}}{{baseName}}{{/isPathParam}}{{^isPathParam}}{{paramName}}{{/isPathParam}}: {{>param_type}} = {{#isPathParam}}Path{{/isPathParam}}{{#isHeaderParam}}Header{{/isHeaderParam}}{{#isFormParam}}Form{{/isFormParam}}{{#isQueryParam}}Query{{/isQueryParam}}{{#isCookieParam}}Cookie{{/isCookieParam}}{{#isBodyParam}}Body{{/isBodyParam}}({{&defaultValue}}{{^defaultValue}}{{#isPathParam}}...{{/isPathParam}}{{^isPathParam}}None{{/isPathParam}}{{/defaultValue}}, description="{{description}}"{{#isQueryParam}}, alias="{{baseName}}"{{/isQueryParam}}{{#isLong}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isLong}}{{#isInteger}}{{#minimum}}, ge={{.}}{{/minimum}}{{#maximum}}, le={{.}}{{/maximum}}{{/isInteger}}{{#vendorExtensions.x-regex}}, regex=r"{{.}}"{{/vendorExtensions.x-regex}}{{#minLength}}, min_length={{.}}{{/minLength}}{{#maxLength}}, max_length={{.}}{{/maxLength}})
\ No newline at end of file
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonFastapiCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonFastapiCodegenTest.java
index 9a222ac9fae3..33b9d46555c5 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonFastapiCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonFastapiCodegenTest.java
@@ -53,4 +53,22 @@ public void testEndpointSpecsWithoutDescription() throws IOException {
         TestUtils.assertFileContains(Paths.get(output + "/src/nodesc/apis/desc_api.py"),
                 "return await BaseDescApi.subclasses[0]().desc()\n");
     }
+
+    @Test
+    public void testNoAdditionalSlashesInQueryRegex() throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("python-fastapi")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"))
+                .setInputSpec("src/test/resources/3_1/issue_19823.yaml");
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+        TestUtils.assertFileContains(Paths.get(output + "/src/openapi_server/apis/default_api.py"),
+                "r\"^[a-zA-Z0-9]+[a-zA-Z0-9\\.\\-_]*[a-zA-Z0-9]+$\"");
+    }
 }
diff --git a/modules/openapi-generator/src/test/resources/3_1/issue_19823.yaml b/modules/openapi-generator/src/test/resources/3_1/issue_19823.yaml
new file mode 100644
index 000000000000..5139ef2a6644
--- /dev/null
+++ b/modules/openapi-generator/src/test/resources/3_1/issue_19823.yaml
@@ -0,0 +1,21 @@
+openapi: 3.1.0
+info:
+  title: test
+  version: 0.0.1
+paths:
+  /v1/test:
+    post:
+      operationId: test
+      parameters:
+        - in: query
+          name: test
+          schema:
+            type: string
+            pattern: '^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$'
+      responses:
+        "200":
+          description: test
+          content:
+            application/json:
+              schema:
+                type: string
\ No newline at end of file
diff --git a/samples/server/petstore/python-fastapi/src/openapi_server/apis/user_api.py b/samples/server/petstore/python-fastapi/src/openapi_server/apis/user_api.py
index 47fd026bbc6e..e7d5ea8011b5 100644
--- a/samples/server/petstore/python-fastapi/src/openapi_server/apis/user_api.py
+++ b/samples/server/petstore/python-fastapi/src/openapi_server/apis/user_api.py
@@ -110,7 +110,7 @@ async def create_users_with_list_input(
     response_model_by_alias=True,
 )
 async def login_user(
-    username: Annotated[str, Field(strict=True, description="The user name for login")] = Query(None, description="The user name for login", alias="username", regex=r"/^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$/"),
+    username: Annotated[str, Field(strict=True, description="The user name for login")] = Query(None, description="The user name for login", alias="username", regex=r"^[a-zA-Z0-9]+[a-zA-Z0-9\.\-_]*[a-zA-Z0-9]+$"),
     password: Annotated[StrictStr, Field(description="The password for login in clear text")] = Query(None, description="The password for login in clear text", alias="password"),
 ) -> str:
     """"""