diff --git a/Android.bp b/Android.bp
index 8282d87..6d3ab86 100644
--- a/Android.bp
+++ b/Android.bp
@@ -46,7 +46,7 @@
         },
     },
 
-    header_libs: ["jni_headers"],
+    header_libs: ["jni_headers", "jni_platform_headers"],
     export_header_lib_headers: ["jni_headers"],
 
     shared_libs: [
@@ -73,6 +73,7 @@
         "include/nativehelper", // TODO(b/63762847): remove
     ],
     cflags: ["-Werror"],
+    include_dirs: ["libnativehelper/platform_include"],
     srcs: [
         "JNIHelp.cpp",
         "JniConstants.cpp",
diff --git a/JNIHelp-priv.h b/JNIHelp-priv.h
new file mode 100644
index 0000000..ce350a5
--- /dev/null
+++ b/JNIHelp-priv.h
@@ -0,0 +1,26 @@
+/*
+ * Copyright 2017 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.
+ */
+
+#ifndef NATIVEHELPER_JNIHELP_PRIV_H_
+#define NATIVEHELPER_JNIHELP_PRIV_H_
+
+namespace android {
+
+void ClearJNIHelpLocalCache();
+
+}  // namespace android
+
+#endif  // JNIHELP_PRIV
diff --git a/JNIHelp.cpp b/JNIHelp.cpp
index 5aefd42..9c6cd74 100644
--- a/JNIHelp.cpp
+++ b/JNIHelp.cpp
@@ -34,6 +34,55 @@
 
 #include <string>
 
+namespace {
+
+// java.io.FileDescriptor.descriptor.
+jfieldID fileDescriptorDescriptorField = nullptr;
+
+// void java.io.FileDescriptor.<init>().
+jmethodID fileDescriptorInitMethod = nullptr;
+// Object java.lang.ref.Reference.get()
+jmethodID referenceGetMethod = nullptr;
+
+jfieldID FindField(JNIEnv* env, jclass klass, const char* name, const char* desc) {
+    jfieldID result = env->GetFieldID(klass, name, desc);
+    if (result == NULL) {
+        ALOGV("failed to find field '%s:%s'", name, desc);
+        abort();
+    }
+    return result;
+}
+
+jmethodID FindMethod(JNIEnv* env, jclass klass, const char* name, const char* signature) {
+    jmethodID result = env->GetMethodID(klass, name, signature);
+    if (result == NULL) {
+        ALOGV("failed to find method '%s%s'", name, signature);
+        abort();
+    }
+    return result;
+}
+
+void InitFieldsAndMethods(JNIEnv* env) {
+    JniConstants::init(env);  // Ensure that classes are cached.
+    fileDescriptorDescriptorField = FindField(env, JniConstants::fileDescriptorClass, "descriptor",
+            "I");
+    fileDescriptorInitMethod = FindMethod(env, JniConstants::fileDescriptorClass, "<init>", "()V");
+    referenceGetMethod = FindMethod(env, JniConstants::referenceClass, "get",
+            "()Ljava/lang/Object;");
+}
+
+}
+
+namespace android {
+
+void ClearJNIHelpLocalCache() {
+    fileDescriptorDescriptorField = nullptr;
+    fileDescriptorInitMethod = nullptr;
+    referenceGetMethod = nullptr;
+}
+
+}
+
 /**
  * Equivalent to ScopedLocalRef, but for C_JNIEnv instead. (And slightly more powerful.)
  */
@@ -326,9 +375,11 @@
 
 jobject jniCreateFileDescriptor(C_JNIEnv* env, int fd) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
-    JniConstants::init(e);
-    static jmethodID ctor = e->GetMethodID(JniConstants::fileDescriptorClass, "<init>", "()V");
-    jobject fileDescriptor = (*env)->NewObject(e, JniConstants::fileDescriptorClass, ctor);
+    if (fileDescriptorInitMethod == nullptr) {
+        InitFieldsAndMethods(e);
+    }
+    jobject fileDescriptor = (*env)->NewObject(e, JniConstants::fileDescriptorClass,
+            fileDescriptorInitMethod);
     // NOTE: NewObject ensures that an OutOfMemoryError will be seen by the Java
     // caller if the alloc fails, so we just return NULL when that happens.
     if (fileDescriptor != NULL)  {
@@ -339,10 +390,12 @@
 
 int jniGetFDFromFileDescriptor(C_JNIEnv* env, jobject fileDescriptor) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
-    JniConstants::init(e);
-    static jfieldID fid = e->GetFieldID(JniConstants::fileDescriptorClass, "descriptor", "I");
+    if (fileDescriptorDescriptorField == nullptr) {
+        InitFieldsAndMethods(e);
+    }
     if (fileDescriptor != NULL) {
-        return (*env)->GetIntField(e, fileDescriptor, fid);
+        return (*env)->GetIntField(e, fileDescriptor,
+                fileDescriptorDescriptorField);
     } else {
         return -1;
     }
@@ -350,16 +403,18 @@
 
 void jniSetFileDescriptorOfFD(C_JNIEnv* env, jobject fileDescriptor, int value) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
-    JniConstants::init(e);
-    static jfieldID fid = e->GetFieldID(JniConstants::fileDescriptorClass, "descriptor", "I");
-    (*env)->SetIntField(e, fileDescriptor, fid, value);
+    if (fileDescriptorDescriptorField == nullptr) {
+        InitFieldsAndMethods(e);
+    }
+    (*env)->SetIntField(e, fileDescriptor, fileDescriptorDescriptorField, value);
 }
 
 jobject jniGetReferent(C_JNIEnv* env, jobject ref) {
     JNIEnv* e = reinterpret_cast<JNIEnv*>(env);
-    JniConstants::init(e);
-    static jmethodID get = e->GetMethodID(JniConstants::referenceClass, "get", "()Ljava/lang/Object;");
-    return (*env)->CallObjectMethod(e, ref, get);
+    if (referenceGetMethod == nullptr) {
+        InitFieldsAndMethods(e);
+    }
+    return (*env)->CallObjectMethod(e, ref, referenceGetMethod);
 }
 
 jstring jniCreateString(C_JNIEnv* env, const jchar* unicodeChars, jsize len) {
diff --git a/JniConstants.cpp b/JniConstants.cpp
index f42de2f..632e40c 100644
--- a/JniConstants.cpp
+++ b/JniConstants.cpp
@@ -17,7 +17,9 @@
 #define LOG_TAG "JniConstants"
 
 #include "ALog-priv.h"
+#include "JNIHelp-priv.h"
 #include <nativehelper/JniConstants.h>
+#include <nativehelper/JniConstants-priv.h>
 #include <nativehelper/ScopedLocalRef.h>
 
 #include <stdlib.h>
@@ -138,3 +140,12 @@
 
     g_constants_initialized = true;
 }
+
+namespace android {
+
+void ClearJniConstantsCache() {
+    g_constants_initialized = false;
+    ClearJNIHelpLocalCache();
+}
+
+}
diff --git a/platform_include/nativehelper/JniConstants-priv.h b/platform_include/nativehelper/JniConstants-priv.h
new file mode 100644
index 0000000..c4cba7c
--- /dev/null
+++ b/platform_include/nativehelper/JniConstants-priv.h
@@ -0,0 +1,26 @@
+/*
+ * Copyright 2017 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.
+ */
+
+#ifndef NATIVEHELPER_PLATFORM_INCLUDE_NATIVEHELPER_JNICONSTANTS_PRIV_H_
+#define NATIVEHELPER_PLATFORM_INCLUDE_NATIVEHELPER_JNICONSTANTS_PRIV_H_
+
+namespace android {
+
+void ClearJniConstantsCache();
+
+}  // namespace android
+
+#endif  // NATIVEHELPER_PLATFORM_INCLUDE_NATIVEHELPER_JNICONSTANTS_PRIV_H_