diff --git a/lib/jasmine-core/jasmine.js b/lib/jasmine-core/jasmine.js
index 4f7c6a91..f2230d10 100644
--- a/lib/jasmine-core/jasmine.js
+++ b/lib/jasmine-core/jasmine.js
@@ -118,6 +118,9 @@ var getJasmineRequireObj = (function() {
     j$.private.matchers = jRequire.requireMatchers(jRequire, j$);
     j$.private.asyncMatchers = jRequire.requireAsyncMatchers(jRequire, j$);
 
+    j$.private.loadedAsBrowserEsm =
+      globalThis.document && !globalThis.document.currentScript;
+
     return j$;
   };
 
@@ -1594,6 +1597,14 @@ getJasmineRequireObj().Env = function(j$) {
     this.execute = async function(runablesToRun) {
       installGlobalErrors();
 
+      // Karma incorrectly loads jasmine-core as an ES module. It isn't one,
+      // and we don't test that configuration. Warn about it.
+      if (j$.private.loadedAsBrowserEsm) {
+        this.deprecated(
+          "jasmine-core isn't an ES module but it was loaded as one. This is not a supported configuration."
+        );
+      }
+
       if (parallelLoadingState) {
         validateConfigForParallel();
       }
diff --git a/src/core/Env.js b/src/core/Env.js
index 52eefbe7..ad39d25c 100644
--- a/src/core/Env.js
+++ b/src/core/Env.js
@@ -402,6 +402,14 @@ getJasmineRequireObj().Env = function(j$) {
     this.execute = async function(runablesToRun) {
       installGlobalErrors();
 
+      // Karma incorrectly loads jasmine-core as an ES module. It isn't one,
+      // and we don't test that configuration. Warn about it.
+      if (j$.private.loadedAsBrowserEsm) {
+        this.deprecated(
+          "jasmine-core isn't an ES module but it was loaded as one. This is not a supported configuration."
+        );
+      }
+
       if (parallelLoadingState) {
         validateConfigForParallel();
       }
diff --git a/src/core/requireCore.js b/src/core/requireCore.js
index fc63800b..77d45121 100644
--- a/src/core/requireCore.js
+++ b/src/core/requireCore.js
@@ -94,6 +94,9 @@ var getJasmineRequireObj = (function() {
     j$.private.matchers = jRequire.requireMatchers(jRequire, j$);
     j$.private.asyncMatchers = jRequire.requireAsyncMatchers(jRequire, j$);
 
+    j$.private.loadedAsBrowserEsm =
+      globalThis.document && !globalThis.document.currentScript;
+
     return j$;
   };