diff --git a/packages/legacy-client/changelog/@unreleased/pr-23.v2.yml b/packages/legacy-client/changelog/@unreleased/pr-23.v2.yml
new file mode 100644
index 000000000..34e44cd06
--- /dev/null
+++ b/packages/legacy-client/changelog/@unreleased/pr-23.v2.yml
@@ -0,0 +1,5 @@
+type: fix
+fix:
+  description: action params type fix
+  links:
+  - https://github.com/palantir/osdk-ts/pull/23
diff --git a/packages/legacy-client/src/client/actions/actions.test.ts b/packages/legacy-client/src/client/actions/actions.test.ts
index d73b89fc8..a96619d81 100644
--- a/packages/legacy-client/src/client/actions/actions.test.ts
+++ b/packages/legacy-client/src/client/actions/actions.test.ts
@@ -32,14 +32,13 @@ import {
   it,
   vi,
 } from "vitest";
-import {
-  type ActionError,
-  ActionExecutionMode,
-  type ActionExecutionOptions,
-  type ActionResponseFromOptions,
-  type Edits,
-  type Result,
-  ReturnEditsMode,
+import { ActionExecutionMode, ReturnEditsMode } from "../..";
+import type {
+  ActionError,
+  ActionExecutionOptions,
+  ActionResponseFromOptions,
+  Edits,
+  Result,
 } from "../..";
 import { USER_AGENT } from "../../USER_AGENT";
 import {
@@ -49,7 +48,7 @@ import {
 import { unwrapResultOrThrow } from "../../util/test/resultUtils";
 import { createBaseOsdkObjectSet } from "../objectSets/OsdkObjectSet";
 import type { OsdkLegacyObjectFrom } from "../OsdkLegacyObject";
-import { type Actions } from "./actions";
+import type { Actions } from "./actions";
 import { createActionProxy } from "./createActionProxy";
 
 describe("Actions", () => {
@@ -73,7 +72,7 @@ describe("Actions", () => {
 
   describe("type tests", () => {
     it("creates proper parameters", async () => {
-      expectTypeOf<Parameters<typeof actions.createTask>>().toMatchTypeOf<
+      expectTypeOf<Parameters<typeof actions.createTask>>().toEqualTypeOf<
         [
           {
             id?: number;
@@ -82,6 +81,10 @@ describe("Actions", () => {
         ]
       >();
 
+      expectTypeOf<typeof actions.createTask>()
+        // @ts-expect-error
+        .toBeCallableWith([{ id: 1 }]);
+
       expectTypeOf<ReturnType<typeof actions.createTask>>().toMatchTypeOf<
         Promise<
           Result<
diff --git a/packages/legacy-client/src/client/actions/actions.ts b/packages/legacy-client/src/client/actions/actions.ts
index 04bf08509..33e3a8015 100644
--- a/packages/legacy-client/src/client/actions/actions.ts
+++ b/packages/legacy-client/src/client/actions/actions.ts
@@ -46,20 +46,23 @@ export type ActionArgs<
   O extends OntologyDefinition<any>,
   A extends keyof O["actions"],
 > =
-  & {
-    [P in NullableKeys<O["actions"][A]["parameters"]>]?: ActionParameterType<
-      O,
-      A,
-      P
-    >;
-  }
-  & {
-    [P in NonNullableKeys<O["actions"][A]["parameters"]>]: ActionParameterType<
-      O,
-      A,
-      P
-    >;
-  };
+  & (NonNullableKeys<O["actions"][A]["parameters"]> extends never ? {}
+    : {
+      [P in NonNullableKeys<O["actions"][A]["parameters"]>]:
+        ActionParameterType<
+          O,
+          A,
+          P
+        >;
+    })
+  & (NullableKeys<O["actions"][A]["parameters"]> extends never ? {}
+    : {
+      [P in NullableKeys<O["actions"][A]["parameters"]>]?: ActionParameterType<
+        O,
+        A,
+        P
+      >;
+    });
 
 export type ActionParameterType<
   O extends OntologyDefinition<any>,
diff --git a/packages/legacy-client/src/client/queries.test.ts b/packages/legacy-client/src/client/queries.test.ts
index 8bb853f3a..f57df4818 100644
--- a/packages/legacy-client/src/client/queries.test.ts
+++ b/packages/legacy-client/src/client/queries.test.ts
@@ -333,6 +333,18 @@ describe("Queries", () => {
           LocalDate
         >;
       }]>();
+
+      expectTypeOf<
+        Parameters<Queries<typeof MockOntology>["queryWithOnlyOptionalArgs"]>
+      >().toEqualTypeOf<[{ string?: string }]>();
+
+      expectTypeOf<
+        Parameters<Queries<typeof MockOntology>["queryWithOnlyRequiredArgs"]>
+      >().toEqualTypeOf<[{ string: string }]>();
+
+      expectTypeOf<typeof queries.queryWithOnlyOptionalArgs>()
+        // @ts-expect-error
+        .toBeCallableWith([{ string: "test" }]);
     });
   });
 
@@ -344,6 +356,8 @@ describe("Queries", () => {
         "queryReturnsAggregation",
         "queryTakesAllParameterTypes",
         "queryTakesNestedObjects",
+        "queryWithOnlyOptionalArgs",
+        "queryWithOnlyRequiredArgs",
       ]
     `);
   });
diff --git a/packages/legacy-client/src/client/queries.ts b/packages/legacy-client/src/client/queries.ts
index 0bd97d750..4d99d2e02 100644
--- a/packages/legacy-client/src/client/queries.ts
+++ b/packages/legacy-client/src/client/queries.ts
@@ -83,20 +83,20 @@ export type QueryArgs<
   O extends OntologyDefinition<any>,
   Q extends QueryNamesFrom<O>,
 > =
-  & {
+  & (NonNullableArgKeys<QueryParameters<O, Q>> extends never ? {} : {
     [P in NonNullableArgKeys<QueryParameters<O, Q>>]: QueryDataType<
       O,
       QueryParameters<O, Q>[P],
       false
     >;
-  }
-  & {
+  })
+  & (NullableArgKeys<QueryParameters<O, Q>> extends never ? {} : {
     [P in NullableArgKeys<QueryParameters<O, Q>>]?: QueryDataType<
       O,
       QueryParameters<O, Q>[P],
       false
     >;
-  };
+  });
 
 export type QueryNamesFrom<O extends OntologyDefinition<any>> =
   keyof O["queries"];
diff --git a/packages/shared.test/changelog/@unreleased/pr-23.v2.yml b/packages/shared.test/changelog/@unreleased/pr-23.v2.yml
new file mode 100644
index 000000000..34e44cd06
--- /dev/null
+++ b/packages/shared.test/changelog/@unreleased/pr-23.v2.yml
@@ -0,0 +1,5 @@
+type: fix
+fix:
+  description: action params type fix
+  links:
+  - https://github.com/palantir/osdk-ts/pull/23
diff --git a/packages/shared.test/src/mock-ontology/mockOntology.ts b/packages/shared.test/src/mock-ontology/mockOntology.ts
index c414bdc0b..e219874a7 100644
--- a/packages/shared.test/src/mock-ontology/mockOntology.ts
+++ b/packages/shared.test/src/mock-ontology/mockOntology.ts
@@ -257,6 +257,30 @@ export const MockOntology = {
         },
       },
     },
+    queryWithOnlyOptionalArgs: {
+      apiName: "queryWithOnlyOptionalArgs",
+      description: "a query that only has optional args",
+      version: "version",
+      output: { type: "boolean" },
+      parameters: {
+        string: {
+          type: "string",
+          nullable: true,
+        },
+      },
+    },
+    queryWithOnlyRequiredArgs: {
+      apiName: "queryWithOnlyRequiredArgs",
+      description: "a query that only has required args",
+      version: "version",
+      output: { type: "boolean" },
+      parameters: {
+        string: {
+          type: "string",
+          nullable: false,
+        },
+      },
+    },
   },
 } satisfies OntologyDefinition<
   | "Task"