diff --git a/src/__tests__/classMap.test.ts b/src/__tests__/classMap.test.ts
index 42e0a5de..9ead322c 100644
--- a/src/__tests__/classMap.test.ts
+++ b/src/__tests__/classMap.test.ts
@@ -16,24 +16,11 @@ describe(makeClassMap, () => {
     expect(makeClassMap(functions)).toStrictEqual<AppMap.ClassMap>([
       {
         type: "package",
-        name: "foo",
-        children: [
-          {
-            type: "class",
-            name: "foo",
-            children: [
-              { type: "function", name: "foo", static: true, location: "/test/app/src/foo.js:3" },
-            ],
-          },
-        ],
-      },
-      {
-        type: "package",
-        name: "util",
+        name: "src",
         children: [
           {
             type: "package",
-            name: "other",
+            name: "util",
             children: [
               {
                 type: "class",
@@ -49,6 +36,13 @@ describe(makeClassMap, () => {
               },
             ],
           },
+          {
+            type: "class",
+            name: "foo",
+            children: [
+              { type: "function", name: "foo", static: true, location: "/test/app/src/foo.js:3" },
+            ],
+          },
           {
             type: "class",
             name: "util",
@@ -110,7 +104,7 @@ function f(
     id,
     params: [],
     static: static_,
-    klassOrPkg: klass,
+    klassOrFile: klass,
     location,
   };
 }
diff --git a/src/__tests__/registry.test.ts b/src/__tests__/registry.test.ts
index 9cce8c28..ed02132e 100644
--- a/src/__tests__/registry.test.ts
+++ b/src/__tests__/registry.test.ts
@@ -21,7 +21,7 @@ describe(registry.createFunctionInfo, () => {
       params: [],
       location: { path: "test.js", lineno: 42 },
       static: true,
-      klassOrPkg: "test",
+      klassOrFile: "test",
     });
   });
 });
@@ -56,7 +56,7 @@ describe(registry.createMethodInfo, () => {
       generator: false,
       params: [],
       id: "testMethod",
-      klassOrPkg: "TestClass",
+      klassOrFile: "TestClass",
       location: undefined,
       static: false,
     });
diff --git a/src/classMap.ts b/src/classMap.ts
index 4dc49edf..ac0ecf3b 100644
--- a/src/classMap.ts
+++ b/src/classMap.ts
@@ -14,15 +14,14 @@ export function makeClassMap(funs: Iterable<FunctionInfo>): AppMap.ClassMap {
   for (const fun of sortFunctions(funs)) {
     if (!fun.location) continue;
     const pkgs = fun.location.path.replace(/\..+$/, "").split(sep).reverse();
-    assert(pkgs.length > 0);
+    if (pkgs.length > 1) pkgs.shift(); // remove the file name (e.g. "foo.js")
 
     let [tree, classes]: FNode = [root, {}];
-    let pkg = "";
     while (pkgs.length > 0) {
-      pkg = pkgs.pop()!;
+      const pkg = pkgs.pop()!;
       [tree, classes] = tree[pkg] ||= [{}, {}];
     }
-    (classes[fun.klassOrPkg] ||= []).push(fun);
+    (classes[fun.klassOrFile] ||= []).push(fun);
   }
 
   let result = makeTree(root);
diff --git a/src/event.ts b/src/event.ts
index 713a8c1b..ab4bb22b 100644
--- a/src/event.ts
+++ b/src/event.ts
@@ -19,7 +19,7 @@ export function makeCallEvent(
     static: !thisArg,
     receiver: optParameter(thisArg),
     parameters: resolveParameters(args, fun),
-    defined_class: fun.klassOrPkg,
+    defined_class: fun.klassOrFile,
     ...fun.location,
   });
 }
diff --git a/src/hooks/__tests__/instrument.test.ts b/src/hooks/__tests__/instrument.test.ts
index 5ed8d88e..23a894d2 100644
--- a/src/hooks/__tests__/instrument.test.ts
+++ b/src/hooks/__tests__/instrument.test.ts
@@ -46,7 +46,7 @@ describe(instrument.transform, () => {
             "path": "test.js",
             "lineno": 2
           },
-          "klassOrPkg": "test",
+          "klassOrFile": "test",
           "static": true
         }];
 
@@ -64,7 +64,7 @@ describe(instrument.transform, () => {
       generator: false,
       location: { path: "test.js", lineno: 2 },
       static: true,
-      klassOrPkg: "test",
+      klassOrFile: "test",
     });
   });
 
@@ -91,7 +91,7 @@ describe(instrument.transform, () => {
             "name": "value"
           }],
           "static": false,
-          "klassOrPkg": "TestClass",
+          "klassOrFile": "TestClass",
           "location": {
             "path": "test.js",
             "lineno": 3
@@ -110,7 +110,7 @@ describe(instrument.transform, () => {
     expect(instrument.transformedFunctionInfos[0]).toStrictEqual<registry.FunctionInfo>({
       params: [{ type: "Identifier", name: "value" }],
       id: "foo",
-      klassOrPkg: "TestClass",
+      klassOrFile: "TestClass",
       static: false,
       async: false,
       generator: false,
diff --git a/src/registry.ts b/src/registry.ts
index 6f6635bc..778dee9a 100644
--- a/src/registry.ts
+++ b/src/registry.ts
@@ -14,7 +14,7 @@ export interface FunctionInfo {
   params: ESTree.Parameter[];
   static: boolean;
   /** Class name, or the package name for a free function */
-  klassOrPkg: string;
+  klassOrFile: string;
   location?: SourceLocation;
 }
 
@@ -31,7 +31,7 @@ export function createFunctionInfo(
     id: id.name,
     params: params.map(stripLocation),
     location,
-    klassOrPkg: pkgOfPath(location.path),
+    klassOrFile: pkgOfPath(location.path),
     static: true,
   };
   return info;
@@ -52,7 +52,7 @@ export function createMethodInfo(
     id: key.name,
     params: params.map(stripLocation),
     static: method.static,
-    klassOrPkg: klass.id.name,
+    klassOrFile: klass.id.name,
     location,
   };
   return info;
diff --git a/test/__snapshots__/httpClient.test.ts.snap b/test/__snapshots__/httpClient.test.ts.snap
index 33331a77..955284ed 100644
--- a/test/__snapshots__/httpClient.test.ts.snap
+++ b/test/__snapshots__/httpClient.test.ts.snap
@@ -83,7 +83,7 @@ exports[`mapping http client requests (ESM) 1`] = `
           "type": "class",
         },
       ],
-      "name": "esm",
+      "name": "httpClient",
       "type": "package",
     },
   ],
@@ -192,7 +192,7 @@ exports[`mapping http client requests 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "httpClient",
       "type": "package",
     },
   ],
@@ -360,7 +360,7 @@ exports[`mapping mocked http client requests 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "httpClient",
       "type": "package",
     },
   ],
diff --git a/test/__snapshots__/httpServer.test.ts.snap b/test/__snapshots__/httpServer.test.ts.snap
index c48aa866..b7af8de9 100644
--- a/test/__snapshots__/httpServer.test.ts.snap
+++ b/test/__snapshots__/httpServer.test.ts.snap
@@ -19,7 +19,7 @@ exports[`mapping Express.js requests 1`] = `
             "type": "class",
           },
         ],
-        "name": "express",
+        "name": "httpServer",
         "type": "package",
       },
     ],
@@ -180,7 +180,7 @@ exports[`mapping Express.js requests 1`] = `
             "type": "class",
           },
         ],
-        "name": "express",
+        "name": "httpServer",
         "type": "package",
       },
     ],
@@ -351,7 +351,7 @@ exports[`mapping Express.js requests 1`] = `
             "type": "class",
           },
         ],
-        "name": "express",
+        "name": "httpServer",
         "type": "package",
       },
     ],
@@ -633,7 +633,7 @@ exports[`mapping Express.js requests with remote recording 1`] = `
           "type": "class",
         },
       ],
-      "name": "express",
+      "name": "httpServer",
       "type": "package",
     },
   ],
diff --git a/test/__snapshots__/mocha.test.ts.snap b/test/__snapshots__/mocha.test.ts.snap
index 14c3a258..ab60ec18 100644
--- a/test/__snapshots__/mocha.test.ts.snap
+++ b/test/__snapshots__/mocha.test.ts.snap
@@ -19,7 +19,7 @@ exports[`mapping Mocha tests 1`] = `
             "type": "class",
           },
         ],
-        "name": "test",
+        "name": "mocha",
         "type": "package",
       },
     ],
@@ -92,7 +92,7 @@ exports[`mapping Mocha tests 1`] = `
             "type": "class",
           },
         ],
-        "name": "calc",
+        "name": "mocha",
         "type": "package",
       },
     ],
@@ -173,7 +173,7 @@ exports[`mapping Mocha tests 1`] = `
             "type": "class",
           },
         ],
-        "name": "calc",
+        "name": "mocha",
         "type": "package",
       },
     ],
diff --git a/test/__snapshots__/mysql.test.ts.snap b/test/__snapshots__/mysql.test.ts.snap
index 6115a1b0..56a2961e 100644
--- a/test/__snapshots__/mysql.test.ts.snap
+++ b/test/__snapshots__/mysql.test.ts.snap
@@ -18,7 +18,7 @@ exports[`mapping MySQL tests 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "mysql",
       "type": "package",
     },
   ],
diff --git a/test/__snapshots__/next.test.ts.snap b/test/__snapshots__/next.test.ts.snap
index 1be0d34d..c145a006 100644
--- a/test/__snapshots__/next.test.ts.snap
+++ b/test/__snapshots__/next.test.ts.snap
@@ -19,7 +19,7 @@ exports[`mapping a Next.js appmap 1`] = `
             "type": "class",
           },
         ],
-        "name": "route",
+        "name": "hello",
         "type": "package",
       },
     ],
diff --git a/test/__snapshots__/postgres.test.ts.snap b/test/__snapshots__/postgres.test.ts.snap
index 33f18a8a..9dcf418f 100644
--- a/test/__snapshots__/postgres.test.ts.snap
+++ b/test/__snapshots__/postgres.test.ts.snap
@@ -18,7 +18,7 @@ exports[`mapping PostgreSQL tests 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "postgres",
       "type": "package",
     },
   ],
diff --git a/test/__snapshots__/simple.test.ts.snap b/test/__snapshots__/simple.test.ts.snap
index fbf73052..53ea8e67 100644
--- a/test/__snapshots__/simple.test.ts.snap
+++ b/test/__snapshots__/simple.test.ts.snap
@@ -29,7 +29,7 @@ exports[`finish signal is handled 1`] = `
           "type": "class",
         },
       ],
-      "name": "server",
+      "name": "simple",
       "type": "package",
     },
   ],
@@ -93,7 +93,7 @@ exports[`forwarding signals to the child 1`] = `
           "type": "class",
         },
       ],
-      "name": "daemon",
+      "name": "simple",
       "type": "package",
     },
   ],
@@ -157,7 +157,7 @@ exports[`mapping a custom Error class with a message property 1`] = `
           "type": "class",
         },
       ],
-      "name": "inspect",
+      "name": "simple",
       "type": "package",
     },
   ],
@@ -244,7 +244,7 @@ exports[`mapping a simple script 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "simple",
       "type": "package",
     },
   ],
@@ -504,7 +504,7 @@ exports[`mapping an extensionless CommonJS file 1`] = `
           "type": "class",
         },
       ],
-      "name": "extensionless",
+      "name": "simple",
       "type": "package",
     },
   ],
@@ -558,7 +558,25 @@ exports[`mapping an mjs script 1`] = `
         {
           "children": [
             {
-              "location": "./index.mjs:1",
+              "children": [
+                {
+                  "location": "./subproject/util.mjs:1",
+                  "name": "twice",
+                  "static": true,
+                  "type": "function",
+                },
+              ],
+              "name": "util",
+              "type": "class",
+            },
+          ],
+          "name": "subproject",
+          "type": "package",
+        },
+        {
+          "children": [
+            {
+              "location": "./index.mjs:3",
               "name": "helloWorld",
               "static": true,
               "type": "function",
@@ -568,7 +586,7 @@ exports[`mapping an mjs script 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "simple",
       "type": "package",
     },
   ],
@@ -577,17 +595,45 @@ exports[`mapping an mjs script 1`] = `
       "defined_class": "index",
       "event": "call",
       "id": 1,
-      "lineno": 1,
+      "lineno": 3,
       "method_id": "helloWorld",
       "parameters": [],
       "path": "./index.mjs",
       "static": true,
       "thread_id": 0,
     },
+    {
+      "defined_class": "util",
+      "event": "call",
+      "id": 2,
+      "lineno": 1,
+      "method_id": "twice",
+      "parameters": [
+        {
+          "class": "Number",
+          "name": "x",
+          "value": "21",
+        },
+      ],
+      "path": "./subproject/util.mjs",
+      "static": true,
+      "thread_id": 0,
+    },
     {
       "elapsed": 31.337,
       "event": "return",
-      "id": 2,
+      "id": 3,
+      "parent_id": 2,
+      "return_value": {
+        "class": "Number",
+        "value": "42",
+      },
+      "thread_id": 0,
+    },
+    {
+      "elapsed": 31.337,
+      "event": "return",
+      "id": 4,
       "parent_id": 1,
       "thread_id": 0,
     },
@@ -632,7 +678,7 @@ exports[`mapping generator functions 1`] = `
           "type": "class",
         },
       ],
-      "name": "generator",
+      "name": "simple",
       "type": "package",
     },
   ],
@@ -725,7 +771,7 @@ exports[`mapping js class methods and constructors containing super keyword 1`]
           "type": "class",
         },
       ],
-      "name": "class",
+      "name": "simple",
       "type": "package",
     },
   ],
diff --git a/test/__snapshots__/sqlite.test.ts.snap b/test/__snapshots__/sqlite.test.ts.snap
index 697e9785..3d9b2923 100644
--- a/test/__snapshots__/sqlite.test.ts.snap
+++ b/test/__snapshots__/sqlite.test.ts.snap
@@ -18,7 +18,7 @@ exports[`mapping Sqlite tests 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "sqlite",
       "type": "package",
     },
   ],
diff --git a/test/__snapshots__/typescript-esm.test.ts.snap b/test/__snapshots__/typescript-esm.test.ts.snap
index 4eb0456c..b04354c1 100644
--- a/test/__snapshots__/typescript-esm.test.ts.snap
+++ b/test/__snapshots__/typescript-esm.test.ts.snap
@@ -18,7 +18,7 @@ exports[`esm-loader is loaded when required 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "typescript-esm",
       "type": "package",
     },
   ],
diff --git a/test/__snapshots__/typescript.test.ts.snap b/test/__snapshots__/typescript.test.ts.snap
index 3a2ef62b..92e93376 100644
--- a/test/__snapshots__/typescript.test.ts.snap
+++ b/test/__snapshots__/typescript.test.ts.snap
@@ -18,7 +18,7 @@ exports[`mapping a simple script 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "typescript",
       "type": "package",
     },
   ],
@@ -92,7 +92,7 @@ exports[`mapping an mts script 1`] = `
           "type": "class",
         },
       ],
-      "name": "index",
+      "name": "typescript",
       "type": "package",
     },
   ],
diff --git a/test/simple/index.mjs b/test/simple/index.mjs
index cde0e819..71ba2bda 100644
--- a/test/simple/index.mjs
+++ b/test/simple/index.mjs
@@ -1,5 +1,7 @@
+import { twice } from "./subproject/util.mjs";
+
 export function helloWorld() {
-  console.log("Hello World from mjs");
+  console.log(`Hello World from mjs: ${twice(21)}`);
 }
 
 helloWorld();
diff --git a/test/simple/subproject/util.mjs b/test/simple/subproject/util.mjs
new file mode 100644
index 00000000..f09ae343
--- /dev/null
+++ b/test/simple/subproject/util.mjs
@@ -0,0 +1,3 @@
+export function twice(x) {
+  return x * 2;
+}