diff --git a/src/cache/inmemory/__tests__/policies.ts b/src/cache/inmemory/__tests__/policies.ts
index e65723a56df..d520ebf5711 100644
--- a/src/cache/inmemory/__tests__/policies.ts
+++ b/src/cache/inmemory/__tests__/policies.ts
@@ -397,7 +397,7 @@ describe("type policies", function () {
       expect(result).toEqual(data);
     });
 
-    it("assumes keyArgs:false when read or merge function present", function () {
+    it("assumes keyArgs:false when read and merge function present", function () {
       const cache = new InMemoryCache({
         typePolicies: {
           TypeA: {
@@ -525,7 +525,7 @@ describe("type policies", function () {
       expect(cache.extract()).toEqual({
         ROOT_QUERY: {
           __typename: "Query",
-          types: [
+          'types({"from":"A","to":"F"})': [
             {
               __typename: "TypeA",
             },
diff --git a/src/cache/inmemory/policies.ts b/src/cache/inmemory/policies.ts
index 3d93bd7e780..22333fc0e37 100644
--- a/src/cache/inmemory/policies.ts
+++ b/src/cache/inmemory/policies.ts
@@ -324,9 +324,12 @@ export class Policies {
             if (typeof merge === "function") existing.merge = merge;
           }
 
-          if (existing.read || existing.merge) {
-            // If we have a read or merge function, assume keyArgs:false
-            // unless existing.keyFn has already been explicitly set.
+          if (existing.read && existing.merge) {
+            // If we have both a read and a merge function, assume
+            // keyArgs:false, because read and merge together can take
+            // responsibility for interpreting arguments in and out. This
+            // default assumption can always be overridden by specifying
+            // keyArgs explicitly in the FieldPolicy.
             existing.keyFn = existing.keyFn || simpleKeyArgsFn;
           }
         });