diff --git a/src/main/java/com/google/devtools/build/lib/bazel/Bazel.java b/src/main/java/com/google/devtools/build/lib/bazel/Bazel.java
index f2829af..b02a1d6 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/Bazel.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/Bazel.java
@@ -43,6 +43,7 @@
           com.google.devtools.build.lib.bazel.BazelWorkspaceStatusModule.class,
           com.google.devtools.build.lib.bazel.BazelDiffAwarenessModule.class,
           com.google.devtools.build.lib.bazel.BazelRepositoryModule.class,
+          com.google.devtools.build.lib.bazel.repository.skylark.SkylarkRepositoryDebugModule.class,
           com.google.devtools.build.lib.bazel.debug.WorkspaceRuleModule.class,
           com.google.devtools.build.lib.bazel.coverage.BazelCoverageReportModule.class,
           com.google.devtools.build.lib.skylarkdebug.module.SkylarkDebuggerModule.class,
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryDebugModule.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryDebugModule.java
new file mode 100644
index 0000000..cd4eae7
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryDebugModule.java
@@ -0,0 +1,70 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.bazel.repository.skylark;
+
+import com.google.common.eventbus.Subscribe;
+import com.google.devtools.build.lib.events.Event;
+import com.google.devtools.build.lib.events.Reporter;
+import com.google.devtools.build.lib.repository.RequestRepositoryInformationEvent;
+import com.google.devtools.build.lib.runtime.BlazeModule;
+import com.google.devtools.build.lib.runtime.CommandEnvironment;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+/**
+ * Module reporting back the place an external repository was defined, if requested by some error
+ * involving that repository. This also covers cases where the definition of the repository is not
+ * directly available, e.g., during detection of a dependency cycle.
+ */
+public final class SkylarkRepositoryDebugModule extends BlazeModule {
+  Map<String, String> repositoryDefinitions;
+  Reporter reporter;
+  Set<String> reported;
+
+  @Override
+  public void beforeCommand(CommandEnvironment env) {
+    repositoryDefinitions = new HashMap<>();
+    reported = new HashSet<>();
+    reporter = env.getReporter();
+    env.getEventBus().register(this);
+  }
+
+  @Override
+  public void afterCommand() {
+    repositoryDefinitions = null;
+    reporter = null;
+    reported = null;
+  }
+
+  @Subscribe
+  public synchronized void definitionLocation(SkylarkRepositoryDefinitionLocationEvent event) {
+    repositoryDefinitions.put(event.getName(), event.getDefinitionInformation());
+  }
+
+  @Subscribe
+  public void requestDefinition(RequestRepositoryInformationEvent event) {
+    String toReport = null;
+    synchronized (this) {
+      if (!reported.contains(event.getName())
+          && repositoryDefinitions.containsKey(event.getName())) {
+        toReport = repositoryDefinitions.get(event.getName());
+      }
+    }
+    if (toReport != null) {
+      reporter.handle(Event.info(toReport));
+    }
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryDefinitionLocationEvent.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryDefinitionLocationEvent.java
new file mode 100644
index 0000000..267bcaa
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryDefinitionLocationEvent.java
@@ -0,0 +1,36 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.bazel.repository.skylark;
+
+import com.google.devtools.build.lib.events.ExtendedEventHandler.ProgressLike;
+
+/** Event reporting about the place where a Starlark repository rule was defined. */
+public class SkylarkRepositoryDefinitionLocationEvent implements ProgressLike {
+
+  private final String name;
+  private final String definitionInformation;
+
+  public SkylarkRepositoryDefinitionLocationEvent(String name, String definitionInformation) {
+    this.name = name;
+    this.definitionInformation = definitionInformation;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public String getDefinitionInformation() {
+    return definitionInformation;
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
index c503bae..5da88d6 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
@@ -70,6 +70,12 @@
       Map<String, String> markerData,
       SkyKey key)
       throws RepositoryFunctionException, InterruptedException {
+    if (rule.getDefinitionInformation() != null) {
+      env.getListener()
+          .post(
+              new SkylarkRepositoryDefinitionLocationEvent(
+                  rule.getName(), rule.getDefinitionInformation()));
+    }
     BaseFunction function = rule.getRuleClassObject().getConfiguredTargetFunction();
     if (declareEnvironmentDependencies(markerData, env, getEnviron(rule)) == null) {
       return null;
diff --git a/src/main/java/com/google/devtools/build/lib/repository/RequestRepositoryInformationEvent.java b/src/main/java/com/google/devtools/build/lib/repository/RequestRepositoryInformationEvent.java
new file mode 100644
index 0000000..ef7eec7
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/repository/RequestRepositoryInformationEvent.java
@@ -0,0 +1,32 @@
+// Copyright 2019 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.repository;
+
+import com.google.devtools.build.lib.events.ExtendedEventHandler.Postable;
+
+/**
+ * Event requesting that additional information, in particular the place of definition, be shown for
+ * a given external repository.
+ */
+public class RequestRepositoryInformationEvent implements Postable {
+  private final String name;
+
+  public RequestRepositoryInformationEvent(String name) {
+    this.name = name;
+  }
+
+  public String getName() {
+    return name;
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkylarkModuleCycleReporter.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkylarkModuleCycleReporter.java
index df84173..37c8958 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkylarkModuleCycleReporter.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkylarkModuleCycleReporter.java
@@ -24,6 +24,7 @@
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.events.ExtendedEventHandler;
 import com.google.devtools.build.lib.packages.WorkspaceFileValue;
+import com.google.devtools.build.lib.repository.RequestRepositoryInformationEvent;
 import com.google.devtools.build.skyframe.CycleInfo;
 import com.google.devtools.build.skyframe.CyclesReporter;
 import com.google.devtools.build.skyframe.SkyKey;
@@ -139,6 +140,15 @@
           };
       AbstractLabelCycleReporter.printCycle(ImmutableList.copyOf(repos), cycleMessage, printer);
       eventHandler.handle(Event.error(null, cycleMessage.toString()));
+      // To help debugging, request that the information be printed about where the respective
+      // repositories were defined.
+      for (SkyKey repo : repos) {
+        if (repo instanceof RepositoryValue.Key) {
+          eventHandler.post(
+              new RequestRepositoryInformationEvent(
+                  ((RepositoryValue.Key) repo).argument().strippedName()));
+        }
+      }
       return true;
     } else if (Iterables.any(cycle, IS_WORKSPACE_FILE)
         || IS_REPOSITORY_DIRECTORY.apply(lastPathElement)
diff --git a/src/test/shell/bazel/external_integration_test.sh b/src/test/shell/bazel/external_integration_test.sh
index 9f64e81..dceeda6 100755
--- a/src/test/shell/bazel/external_integration_test.sh
+++ b/src/test/shell/bazel/external_integration_test.sh
@@ -2073,7 +2073,8 @@
 
 function test_circular_definition_reported() {
   # Verify that bazel reports a useful error message upon
-  # detecting a circular definition of a repository
+  # detecting a circular definition of a repository.
+  # Also verify that the call stack of the definition is shown.
 
   WRKDIR=$(mktemp -d "${TEST_TMPDIR}/testXXXXXX")
   cd "${WRKDIR}"
@@ -2102,20 +2103,32 @@
 
   mkdir main
   cd main
-  cat > WORKSPACE <<EOF
+  cat > foo.bzl <<'EOF'
 load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
-http_archive(
-  name = "a",
-  url = "file://${WRKDIR}/ext.tar",
-  build_file = "@b//:a.BUILD",
-)
+def foo():
+  http_archive(
+    name = "a",
+    url = "file://${WRKDIR}/ext.tar",
+    build_file = "@b//:a.BUILD",
+  )
+EOF
+  cat > bar.bzl <<'EOF'
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
 
-http_archive(
-  name = "b",
-  url = "file://${WRKDIR}/ext.tar",
-  build_file = "@a//:b.BUILD",
-)
+def bar():
+  http_archive(
+    name = "b",
+    url = "file://${WRKDIR}/ext.tar",
+    build_file = "@a//:b.BUILD",
+  )
+EOF
+  cat > WORKSPACE <<EOF
+load("//:foo.bzl", "foo")
+load("//:bar.bzl", "bar")
+
+foo()
+bar()
 
 load("@a//:notabuildfile.bzl", "x")
 EOF
@@ -2128,6 +2141,14 @@
   expect_log '[Cc]ircular definition.*repositor'
   expect_log '@a'
   expect_log '@b'
+
+  # We expect to find the call stack for the definition of the repositories
+  # a and b
+  expect_log "WORKSPACE:4:1"
+  expect_log "foo.bzl:4:3"
+
+  expect_log "WORKSPACE:5:1"
+  expect_log "bar.bzl:4:3"
 }
 
 run_suite "external tests"