diff --git a/libnativeloader/Android.bp b/libnativeloader/Android.bp
index 17983bc..8903b72 100644
--- a/libnativeloader/Android.bp
+++ b/libnativeloader/Android.bp
@@ -23,4 +23,20 @@
         "llndk.libraries.txt",
         "vndksp.libraries.txt",
     ],
+    target: {
+        android: {
+            version_script: "libnativeloader.map.txt",
+        },
+    },
+    stubs: {
+        symbol_file: "libnativeloader.map.txt",
+        versions: ["1"],
+    },
+}
+
+cc_library_headers {
+    name: "libnativeloader-dummy-headers",
+
+    host_supported: true,
+    export_include_dirs: ["include"],
 }
diff --git a/libnativeloader/include/nativeloader/dlext_namespaces.h b/libnativeloader/include/nativeloader/dlext_namespaces.h
index 43c9329..ca026b3 100644
--- a/libnativeloader/include/nativeloader/dlext_namespaces.h
+++ b/libnativeloader/include/nativeloader/dlext_namespaces.h
@@ -18,6 +18,7 @@
 #define __ANDROID_DLEXT_NAMESPACES_H__
 
 #include <android/dlext.h>
+#include <stdbool.h>
 
 __BEGIN_DECLS
 
@@ -84,12 +85,9 @@
  * If a library or any of its dependencies are outside of the permitted_when_isolated_path
  * and search_path, and it is not part of the public namespace dlopen will fail.
  */
-extern struct android_namespace_t* android_create_namespace(const char* name,
-                                                            const char* ld_library_path,
-                                                            const char* default_library_path,
-                                                            uint64_t type,
-                                                            const char* permitted_when_isolated_path,
-                                                            android_namespace_t* parent);
+extern struct android_namespace_t* android_create_namespace(
+    const char* name, const char* ld_library_path, const char* default_library_path, uint64_t type,
+    const char* permitted_when_isolated_path, struct android_namespace_t* parent);
 
 /*
  * Creates a link between namespaces. Every link has list of sonames of
@@ -107,8 +105,8 @@
  *      step will not go deeper into linked namespaces for this library but
  *      will do so for DT_NEEDED libraries.
  */
-extern bool android_link_namespaces(android_namespace_t* from,
-                                    android_namespace_t* to,
+extern bool android_link_namespaces(struct android_namespace_t* from,
+                                    struct android_namespace_t* to,
                                     const char* shared_libs_sonames);
 
 /*
@@ -124,7 +122,7 @@
  */
 extern void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size);
 
-extern android_namespace_t* android_get_exported_namespace(const char* name);
+extern struct android_namespace_t* android_get_exported_namespace(const char* name);
 
 __END_DECLS
 
diff --git a/libnativeloader/include/nativeloader/native_loader.h b/libnativeloader/include/nativeloader/native_loader.h
index c1d9d2a..af53dc5 100644
--- a/libnativeloader/include/nativeloader/native_loader.h
+++ b/libnativeloader/include/nativeloader/native_loader.h
@@ -17,14 +17,21 @@
 #ifndef NATIVE_LOADER_H_
 #define NATIVE_LOADER_H_
 
-#include "jni.h"
+#include <stdbool.h>
 #include <stdint.h>
-#include <string>
+#include "jni.h"
 #if defined(__ANDROID__)
 #include <android/dlext.h>
 #endif
 
+#ifdef __cplusplus
 namespace android {
+extern "C" {
+#endif  // __cplusplus
+
+// README: the char** error message parameter being passed
+// to the methods below need to be freed through calling NativeLoaderFreeErrorMessage.
+// It's the caller's responsibility to call that method.
 
 __attribute__((visibility("default")))
 void InitializeNativeLoader();
@@ -38,42 +45,39 @@
                                    jstring library_path,
                                    jstring permitted_path);
 
-__attribute__((visibility("default")))
-void* OpenNativeLibrary(JNIEnv* env,
-                        int32_t target_sdk_version,
-                        const char* path,
-                        jobject class_loader,
-                        jstring library_path,
-                        bool* needs_native_bridge,
-                        std::string* error_msg);
+__attribute__((visibility("default"))) void* OpenNativeLibrary(
+    JNIEnv* env, int32_t target_sdk_version, const char* path, jobject class_loader,
+    jstring library_path, bool* needs_native_bridge, char** error_msg);
 
 __attribute__((visibility("default"))) bool CloseNativeLibrary(void* handle,
                                                                const bool needs_native_bridge,
-                                                               std::string* error_msg);
+                                                               char** error_msg);
+
+__attribute__((visibility("default"))) void NativeLoaderFreeErrorMessage(char* msg);
 
 #if defined(__ANDROID__)
 // Look up linker namespace by class_loader. Returns nullptr if
 // there is no namespace associated with the class_loader.
 // TODO(b/79940628): move users to FindNativeLoaderNamespaceByClassLoader and remove this function.
-__attribute__((visibility("default")))
-android_namespace_t* FindNamespaceByClassLoader(JNIEnv* env, jobject class_loader);
-// That version works with native bridge namespaces, but requires use of OpenNativeLibrary.
-class NativeLoaderNamespace;
-__attribute__((visibility("default")))
-NativeLoaderNamespace* FindNativeLoaderNamespaceByClassLoader(
+__attribute__((visibility("default"))) struct android_namespace_t* FindNamespaceByClassLoader(
     JNIEnv* env, jobject class_loader);
+// That version works with native bridge namespaces, but requires use of OpenNativeLibrary.
+struct NativeLoaderNamespace;
+__attribute__((visibility("default"))) struct NativeLoaderNamespace*
+FindNativeLoaderNamespaceByClassLoader(JNIEnv* env, jobject class_loader);
 // Load library.  Unlinke OpenNativeLibrary above couldn't create namespace on demand, but does
 // not require access to JNIEnv either.
-__attribute__((visibility("default")))
-void* OpenNativeLibrary(NativeLoaderNamespace* ns,
-                        const char* path,
-                        bool* needs_native_bridge,
-                        std::string* error_msg);
+__attribute__((visibility("default"))) void* OpenNativeLibraryInNamespace(
+    struct NativeLoaderNamespace* ns, const char* path, bool* needs_native_bridge,
+    char** error_msg);
 #endif
 
 __attribute__((visibility("default")))
 void ResetNativeLoader();
 
-};  // namespace android
+#ifdef __cplusplus
+}  // extern "C"
+}  // namespace android
+#endif  // __cplusplus
 
 #endif  // NATIVE_BRIDGE_H_
diff --git a/libnativeloader/libnativeloader.map.txt b/libnativeloader/libnativeloader.map.txt
new file mode 100644
index 0000000..40c30bd
--- /dev/null
+++ b/libnativeloader/libnativeloader.map.txt
@@ -0,0 +1,31 @@
+#
+# Copyright (C) 2019 The Android Open Source Project
+#
+# 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.
+#
+
+# TODO(b/122710865): Prune these uses once the runtime APEX is complete.
+LIBNATIVELOADER_1 {
+  global:
+    OpenNativeLibrary;
+    InitializeNativeLoader;
+    ResetNativeLoader;
+    CloseNativeLibrary;
+    OpenNativeLibraryInNamespace;
+    FindNamespaceByClassLoader;
+    FindNativeLoaderNamespaceByClassLoader;
+    CreateClassLoaderNamespace;
+    NativeLoaderFreeErrorMessage;
+  local:
+    *;
+};
diff --git a/libnativeloader/native_loader.cpp b/libnativeloader/native_loader.cpp
index de7ea08..f231afa 100644
--- a/libnativeloader/native_loader.cpp
+++ b/libnativeloader/native_loader.cpp
@@ -52,7 +52,7 @@
 namespace android {
 
 #if defined(__ANDROID__)
-class NativeLoaderNamespace {
+struct NativeLoaderNamespace {
  public:
   NativeLoaderNamespace()
       : android_ns_(nullptr), native_bridge_ns_(nullptr) { }
@@ -151,14 +151,9 @@
  public:
   LibraryNamespaces() : initialized_(false) { }
 
-  NativeLoaderNamespace* Create(JNIEnv* env,
-                                uint32_t target_sdk_version,
-                                jobject class_loader,
-                                bool is_shared,
-                                bool is_for_vendor,
-                                jstring java_library_path,
-                                jstring java_permitted_path,
-                                std::string* error_msg) {
+  NativeLoaderNamespace* Create(JNIEnv* env, uint32_t target_sdk_version, jobject class_loader,
+                                bool is_shared, bool is_for_vendor, jstring java_library_path,
+                                jstring java_permitted_path, std::string* error_msg) {
     std::string library_path; // empty string by default.
 
     if (java_library_path != nullptr) {
@@ -628,13 +623,9 @@
   return nullptr;
 }
 
-void* OpenNativeLibrary(JNIEnv* env,
-                        int32_t target_sdk_version,
-                        const char* path,
-                        jobject class_loader,
-                        jstring library_path,
-                        bool* needs_native_bridge,
-                        std::string* error_msg) {
+void* OpenNativeLibrary(JNIEnv* env, int32_t target_sdk_version, const char* path,
+                        jobject class_loader, jstring library_path, bool* needs_native_bridge,
+                        char** error_msg) {
 #if defined(__ANDROID__)
   UNUSED(target_sdk_version);
   if (class_loader == nullptr) {
@@ -652,19 +643,16 @@
   if ((ns = g_namespaces->FindNamespaceByClassLoader(env, class_loader)) == nullptr) {
     // This is the case where the classloader was not created by ApplicationLoaders
     // In this case we create an isolated not-shared namespace for it.
-    if ((ns = g_namespaces->Create(env,
-                                   target_sdk_version,
-                                   class_loader,
-                                   false /* is_shared */,
-                                   false /* is_for_vendor */,
-                                   library_path,
-                                   nullptr,
-                                   error_msg)) == nullptr) {
+    std::string create_error_msg;
+    if ((ns = g_namespaces->Create(env, target_sdk_version, class_loader, false /* is_shared */,
+                                   false /* is_for_vendor */, library_path, nullptr,
+                                   &create_error_msg)) == nullptr) {
+      *error_msg = strdup(create_error_msg.c_str());
       return nullptr;
     }
   }
 
-  return OpenNativeLibrary(ns, path, needs_native_bridge, error_msg);
+  return OpenNativeLibraryInNamespace(ns, path, needs_native_bridge, error_msg);
 #else
   UNUSED(env, target_sdk_version, class_loader);
 
@@ -705,35 +693,40 @@
       if (handle != nullptr) {
         return handle;
       }
-      *error_msg = NativeBridgeGetError();
+      *error_msg = strdup(NativeBridgeGetError());
     } else {
-      *error_msg = dlerror();
+      *error_msg = strdup(dlerror());
     }
   }
   return nullptr;
 #endif
 }
 
-bool CloseNativeLibrary(void* handle, const bool needs_native_bridge, std::string* error_msg) {
+bool CloseNativeLibrary(void* handle, const bool needs_native_bridge, char** error_msg) {
   bool success;
   if (needs_native_bridge) {
     success = (NativeBridgeUnloadLibrary(handle) == 0);
     if (!success) {
-      *error_msg = NativeBridgeGetError();
+      *error_msg = strdup(NativeBridgeGetError());
     }
   } else {
     success = (dlclose(handle) == 0);
     if (!success) {
-      *error_msg = dlerror();
+      *error_msg = strdup(dlerror());
     }
   }
 
   return success;
 }
 
+void NativeLoaderFreeErrorMessage(char* msg) {
+  // The error messages get allocated through strdup, so we must call free on them.
+  free(msg);
+}
+
 #if defined(__ANDROID__)
-void* OpenNativeLibrary(NativeLoaderNamespace* ns, const char* path, bool* needs_native_bridge,
-                        std::string* error_msg) {
+void* OpenNativeLibraryInNamespace(NativeLoaderNamespace* ns, const char* path,
+                                   bool* needs_native_bridge, char** error_msg) {
   if (ns->is_android_namespace()) {
     android_dlextinfo extinfo;
     extinfo.flags = ANDROID_DLEXT_USE_NAMESPACE;
@@ -741,14 +734,14 @@
 
     void* handle = android_dlopen_ext(path, RTLD_NOW, &extinfo);
     if (handle == nullptr) {
-      *error_msg = dlerror();
+      *error_msg = strdup(dlerror());
     }
     *needs_native_bridge = false;
     return handle;
   } else {
     void* handle = NativeBridgeLoadLibraryExt(path, RTLD_NOW, ns->get_native_bridge_ns());
     if (handle == nullptr) {
-      *error_msg = NativeBridgeGetError();
+      *error_msg = strdup(NativeBridgeGetError());
     }
     *needs_native_bridge = true;
     return handle;
diff --git a/libnativeloader/test/Android.bp b/libnativeloader/test/Android.bp
index d528f30..1464e39 100644
--- a/libnativeloader/test/Android.bp
+++ b/libnativeloader/test/Android.bp
@@ -69,3 +69,14 @@
         "libbase",
     ],
 }
+
+// Build the test for the C API.
+cc_test {
+    name: "libnativeloader-api-tests",
+    host_supported: true,
+    test_per_src: true,
+    srcs: [
+        "api_test.c",
+    ],
+    header_libs: ["libnativeloader-dummy-headers"],
+}
diff --git a/libnativeloader/test/api_test.c b/libnativeloader/test/api_test.c
new file mode 100644
index 0000000..e7025fd
--- /dev/null
+++ b/libnativeloader/test/api_test.c
@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+/* The main purpose of this test is to ensure this C header compiles in C, so
+ * that no C++ features inadvertently leak into the C ABI. */
+#include "nativeloader/native_loader.h"
+
+int main(int argc, char** argv) {
+  (void)argc;
+  (void)argv;
+  return 0;
+}