diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java
index 85516bc220cbc3..73894018591823 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcCompilationHelper.java
@@ -1222,15 +1222,16 @@ private ImmutableMap<Artifact, String> calculateOutputNameMap(
     for (Artifact source : sourceArtifacts) {
       String outputName =
           FileSystemUtils.removeExtension(source.getRootRelativePath()).getBaseName();
-      count.put(outputName, count.getOrDefault(outputName, 0) + 1);
+      count.put(outputName.toLowerCase(),
+          count.getOrDefault(outputName.toLowerCase(), 0) + 1);
     }
 
     for (Artifact source : sourceArtifacts) {
       String outputName =
           FileSystemUtils.removeExtension(source.getRootRelativePath()).getBaseName();
-      if (count.getOrDefault(outputName, 0) > 1) {
-        int num = number.getOrDefault(outputName, 0);
-        number.put(outputName, num + 1);
+      if (count.getOrDefault(outputName.toLowerCase(), 0) > 1) {
+        int num = number.getOrDefault(outputName.toLowerCase(), 0);
+        number.put(outputName.toLowerCase(), num + 1);
         outputName = num + "/" + outputName;
       }
       // If prefixDir is set, prepend it to the outputName
diff --git a/src/test/java/com/google/devtools/build/lib/rules/cpp/CcLibraryConfiguredTargetTest.java b/src/test/java/com/google/devtools/build/lib/rules/cpp/CcLibraryConfiguredTargetTest.java
index bf9ff66ae49bdd..c509a366de907f 100644
--- a/src/test/java/com/google/devtools/build/lib/rules/cpp/CcLibraryConfiguredTargetTest.java
+++ b/src/test/java/com/google/devtools/build/lib/rules/cpp/CcLibraryConfiguredTargetTest.java
@@ -584,7 +584,7 @@ private void setupPackagesForSourcesWithSameBaseNameTests() throws Exception {
         "foo/BUILD",
         "cc_library(",
         "    name = 'lib',",
-        "    srcs = ['a.cc', 'subpkg/b.cc', 'subpkg/a.c', '//bar:srcs'],",
+        "    srcs = ['a.cc', 'subpkg1/b.cc', 'subpkg1/a.c', '//bar:srcs', 'subpkg2/A.c'],",
         ")");
     scratch.file("bar/BUILD", "filegroup(name = 'srcs', srcs = ['a.cpp'])");
   }
@@ -599,17 +599,20 @@ public void testContainingSourcesWithSameBaseNameWithNewObjPath() throws Excepti
     Artifact a0 = getBinArtifact("_objs/lib/0/a.pic.o", "//foo:lib");
     Artifact a1 = getBinArtifact("_objs/lib/1/a.pic.o", "//foo:lib");
     Artifact a2 = getBinArtifact("_objs/lib/2/a.pic.o", "//foo:lib");
+    Artifact a3 = getBinArtifact("_objs/lib/3/A.pic.o", "//foo:lib");
     Artifact b = getBinArtifact("_objs/lib/b.pic.o", "//foo:lib");
 
     assertThat(getGeneratingAction(a0)).isNotNull();
     assertThat(getGeneratingAction(a1)).isNotNull();
     assertThat(getGeneratingAction(a2)).isNotNull();
+    assertThat(getGeneratingAction(a3)).isNotNull();
     assertThat(getGeneratingAction(b)).isNotNull();
 
     assertThat(getGeneratingAction(a0).getInputs()).contains(getSourceArtifact("foo/a.cc"));
-    assertThat(getGeneratingAction(a1).getInputs()).contains(getSourceArtifact("foo/subpkg/a.c"));
+    assertThat(getGeneratingAction(a1).getInputs()).contains(getSourceArtifact("foo/subpkg1/a.c"));
     assertThat(getGeneratingAction(a2).getInputs()).contains(getSourceArtifact("bar/a.cpp"));
-    assertThat(getGeneratingAction(b).getInputs()).contains(getSourceArtifact("foo/subpkg/b.cc"));
+    assertThat(getGeneratingAction(a3).getInputs()).contains(getSourceArtifact("foo/subpkg2/A.c"));
+    assertThat(getGeneratingAction(b).getInputs()).contains(getSourceArtifact("foo/subpkg1/b.cc"));
   }
 
   @Test
@@ -620,19 +623,22 @@ public void testContainingSourcesWithSameBaseNameWithLegacyObjPath() throws Exce
     getConfiguredTarget("//foo:lib");
 
     Artifact a0 = getBinArtifact("_objs/lib/foo/a.pic.o", "//foo:lib");
-    Artifact a1 = getBinArtifact("_objs/lib/foo/subpkg/a.pic.o", "//foo:lib");
+    Artifact a1 = getBinArtifact("_objs/lib/foo/subpkg1/a.pic.o", "//foo:lib");
     Artifact a2 = getBinArtifact("_objs/lib/bar/a.pic.o", "//foo:lib");
-    Artifact b = getBinArtifact("_objs/lib/foo/subpkg/b.pic.o", "//foo:lib");
+    Artifact a3 = getBinArtifact("_objs/lib/foo/subpkg2/A.pic.o", "//foo:lib");
+    Artifact b = getBinArtifact("_objs/lib/foo/subpkg1/b.pic.o", "//foo:lib");
 
     assertThat(getGeneratingAction(a0)).isNotNull();
     assertThat(getGeneratingAction(a1)).isNotNull();
     assertThat(getGeneratingAction(a2)).isNotNull();
+    assertThat(getGeneratingAction(a3)).isNotNull();
     assertThat(getGeneratingAction(b)).isNotNull();
 
     assertThat(getGeneratingAction(a0).getInputs()).contains(getSourceArtifact("foo/a.cc"));
-    assertThat(getGeneratingAction(a1).getInputs()).contains(getSourceArtifact("foo/subpkg/a.c"));
+    assertThat(getGeneratingAction(a1).getInputs()).contains(getSourceArtifact("foo/subpkg1/a.c"));
     assertThat(getGeneratingAction(a2).getInputs()).contains(getSourceArtifact("bar/a.cpp"));
-    assertThat(getGeneratingAction(b).getInputs()).contains(getSourceArtifact("foo/subpkg/b.cc"));
+    assertThat(getGeneratingAction(a3).getInputs()).contains(getSourceArtifact("foo/subpkg2/A.c"));
+    assertThat(getGeneratingAction(b).getInputs()).contains(getSourceArtifact("foo/subpkg1/b.cc"));
   }
 
   private void setupPackagesForModuleTests(boolean useHeaderModules) throws Exception {