diff --git a/packages/delisp-core/__tests__/infer.ts b/packages/delisp-core/__tests__/infer.ts
index afe5b08a..1f254454 100644
--- a/packages/delisp-core/__tests__/infer.ts
+++ b/packages/delisp-core/__tests__/infer.ts
@@ -225,6 +225,24 @@ describe("Type inference", () => {
       });
     });
 
+    describe("Primitive functions", () => {
+      it("map with multiple values", () => {
+        expect(typeOf("(map (lambda (x) (values x x)) [1 2 3 4])")).toEqual(
+          "[number]"
+        );
+      });
+      it("filter with multiple values", () => {
+        expect(
+          typeOf("(filter (lambda (x) (values true 5)) [-2 -1 0 1 2])")
+        ).toEqual("[number]");
+      });
+      it("fold with multiple values", () => {
+        expect(
+          typeOf(`(fold (lambda (a b) (values 50 (+ a b))) [1 2 3 4] 0)`)
+        ).toEqual("number");
+      });
+    });
+
     describe("Type annotations", () => {
       it("user-specified variables can specialize inferred types", () => {
         expect(typeOf("(the [number] [])")).toBe("[number]");
diff --git a/packages/delisp-core/src/compiler/inline-primitives.ts b/packages/delisp-core/src/compiler/inline-primitives.ts
index 1c733281..f6dacbae 100644
--- a/packages/delisp-core/src/compiler/inline-primitives.ts
+++ b/packages/delisp-core/src/compiler/inline-primitives.ts
@@ -174,13 +174,17 @@ defineInlinePrimitive("*", "(-> number number _ number)", args => {
   };
 });
 
-defineInlinePrimitive("map", "(-> (-> a e b) [a] e [b])", ([fn, vec]) => {
-  return methodCall(vec, "map", [primitiveCall("bindPrimaryValue", fn)]);
-});
+defineInlinePrimitive(
+  "map",
+  "(-> (-> a e (values b | _)) [a] e [b])",
+  ([fn, vec]) => {
+    return methodCall(vec, "map", [primitiveCall("bindPrimaryValue", fn)]);
+  }
+);
 
 defineInlinePrimitive(
   "filter",
-  "(-> (-> a _ boolean) [a] _ [a])",
+  "(-> (-> a _ (values boolean | _)) [a] _ [a])",
   ([predicate, vec]) => {
     return methodCall(vec, "filter", [
       primitiveCall("bindPrimaryValue", predicate)
@@ -190,7 +194,7 @@ defineInlinePrimitive(
 
 defineInlinePrimitive(
   "fold",
-  "(-> (-> b a _ b) [a] b _ b)",
+  "(-> (-> b a _ (values b | _)) [a] b _ b)",
   ([fn, vec, init]) => {
     return methodCall(vec, "reduce", [
       primitiveCall("bindPrimaryValue", fn),