diff --git a/tests/dlopen_test.cpp b/tests/dlopen_test.cpp
index 5ef32ad..5b5c7f6 100644
--- a/tests/dlopen_test.cpp
+++ b/tests/dlopen_test.cpp
@@ -58,6 +58,27 @@
 #endif
 }
 
+static void* ConcurrentDlErrorFn(void* arg) {
+  dlopen("/child/thread", RTLD_NOW);
+  return reinterpret_cast<void*>(strdup(dlerror()));
+}
+
+TEST(dlopen, dlerror_concurrent) {
+  dlopen("/main/thread", RTLD_NOW);
+  const char* main_thread_error = dlerror();
+  ASSERT_SUBSTR("/main/thread", main_thread_error);
+
+  pthread_t t;
+  ASSERT_EQ(0, pthread_create(&t, NULL, ConcurrentDlErrorFn, NULL));
+  void* result;
+  ASSERT_EQ(0, pthread_join(t, &result));
+  char* child_thread_error = static_cast<char*>(result);
+  ASSERT_SUBSTR("/child/thread", child_thread_error);
+  free(child_thread_error);
+
+  ASSERT_SUBSTR("/main/thread", main_thread_error);
+}
+
 TEST(dlopen, dlsym_failures) {
   dlerror(); // Clear any pending errors.
   void* self = dlopen(NULL, RTLD_NOW);
diff --git a/tests/string_test.cpp b/tests/string_test.cpp
index ea1491c..47469d8 100644
--- a/tests/string_test.cpp
+++ b/tests/string_test.cpp
@@ -29,7 +29,7 @@
   ASSERT_STREQ("Unknown error 1234", strerror(1234));
 }
 
-void* ConcurrentStrErrorFn(void* arg) {
+static void* ConcurrentStrErrorFn(void* arg) {
   bool equal = (strcmp("Unknown error 2002", strerror(2002)) == 0);
   return reinterpret_cast<void*>(equal);
 }
@@ -88,7 +88,7 @@
   ASSERT_STREQ("Unknown signal 1234", strsignal(1234)); // Too large.
 }
 
-void* ConcurrentStrSignalFn(void* arg) {
+static void* ConcurrentStrSignalFn(void* arg) {
   bool equal = (strcmp("Unknown signal 2002", strsignal(2002)) == 0);
   return reinterpret_cast<void*>(equal);
 }