diff --git a/test/BUILD.gn b/test/BUILD.gn
index f2632d3f63..ff13621c1e 100644
--- a/test/BUILD.gn
+++ b/test/BUILD.gn
@@ -253,6 +253,7 @@ if (rtc_include_tests) {
 
     deps = [
       ":field_trial",
+      ":fileutils_override_api",
       ":perf_test",
       ":test_support",
       "../rtc_base",
diff --git a/test/test_main_lib.cc b/test/test_main_lib.cc
index bb41e6530f..1650d2ac79 100644
--- a/test/test_main_lib.cc
+++ b/test/test_main_lib.cc
@@ -28,6 +28,7 @@
 #include "test/gmock.h"
 #include "test/gtest.h"
 #include "test/testsupport/file_utils.h"
+#include "test/testsupport/file_utils_override.h"
 #include "test/testsupport/perf_test.h"
 
 #if defined(WEBRTC_WIN)
@@ -80,6 +81,14 @@ ABSL_FLAG(std::vector<std::string>,
 
 #endif
 
+ABSL_FLAG(std::string,
+          resources_dir,
+          "",
+          "Where to look for the runtime dependencies. If not specified, we "
+          "will use a reasonable default depending on where we are running. "
+          "This flag is useful if we copy over test resources to a phone and "
+          "need to tell the tests where their resources are.");
+
 ABSL_FLAG(bool, logs, true, "print logs to stderr");
 ABSL_FLAG(bool, verbose, false, "verbose logs to stderr");
 
@@ -106,6 +115,10 @@ class TestMainImpl : public TestMain {
     ::testing::InitGoogleMock(argc, argv);
     absl::ParseCommandLine(*argc, argv);
 
+    std::string resources_dir = absl::GetFlag(FLAGS_resources_dir);
+    if (!resources_dir.empty())
+      test::internal::OverrideResourcesDir(resources_dir);
+
     // Default to LS_INFO, even for release builds to provide better test
     // logging.
     if (rtc::LogMessage::GetLogToDebug() > rtc::LS_INFO)
diff --git a/test/testsupport/file_utils_override.cc b/test/testsupport/file_utils_override.cc
index 09806913a5..3106d0fe0e 100644
--- a/test/testsupport/file_utils_override.cc
+++ b/test/testsupport/file_utils_override.cc
@@ -150,6 +150,12 @@ std::string ResourcePath(const std::string& name,
 #endif
 }
 
+void OverrideResourcesDir(const std::string& resources_dir) {
+  RTC_CHECK(false)
+      << "Setting the resource dir is not supported in open-source "
+         "tests.";
+}
+
 }  // namespace internal
 }  // namespace test
 }  // namespace webrtc
diff --git a/test/testsupport/file_utils_override.h b/test/testsupport/file_utils_override.h
index a72cd805cf..235c83994b 100644
--- a/test/testsupport/file_utils_override.h
+++ b/test/testsupport/file_utils_override.h
@@ -38,8 +38,7 @@ std::string OutputPath();
 // directory.
 std::string WorkingDir();
 
-// Returns a path to a resource file in [project-root]/resources/ dir.
-// Returns an absolute path
+// Returns a full path to a resource file in the resources_dir dir.
 //
 // Arguments:
 //    name - Name of the resource file. If a plain filename (no directory path)
@@ -49,6 +48,15 @@ std::string WorkingDir();
 //    extension - File extension, without the dot, i.e. "bmp" or "yuv".
 std::string ResourcePath(const std::string& name, const std::string& extension);
 
+// Overrides the root resource dir. See ResourcePath for more information.
+//
+// This is not necessary in most cases, but it can be if we're running on
+// phones and copy over resources to some custom location.
+//
+// Arguments:
+//    resources_dir - Where resources are located.
+void OverrideResourcesDir(const std::string& resources_dir);
+
 }  // namespace internal
 }  // namespace test
 }  // namespace webrtc