diff --git a/src/runtime/java/jni_utils.c b/src/runtime/java/jni_utils.c
index 120233975..59c4a7e54 100644
--- a/src/runtime/java/jni_utils.c
+++ b/src/runtime/java/jni_utils.c
@@ -11,7 +11,7 @@
 #define l2p(x) ((void*) (intptr_t) (x))
 #define p2l(x) ((jlong) (intptr_t) (x))
 
-jstring
+JPGF_INTERNAL jstring
 gu2j_string(JNIEnv *env, GuString s) {
 	const char* utf8 = s;
 	size_t len = strlen(s);
@@ -33,7 +33,7 @@ gu2j_string(JNIEnv *env, GuString s) {
 	return (*env)->NewString(env, utf16, dst-utf16);
 }
 
-jstring
+JPGF_INTERNAL jstring
 gu2j_string_buf(JNIEnv *env, GuStringBuf* sbuf) {
 	const char* s    = gu_string_buf_data(sbuf);
 	const char* utf8 = s;
@@ -56,7 +56,7 @@ gu2j_string_buf(JNIEnv *env, GuStringBuf* sbuf) {
 	return (*env)->NewString(env, utf16, dst-utf16);
 }
 
-GuString
+JPGF_INTERNAL GuString
 j2gu_string(JNIEnv *env, jstring s, GuPool* pool) {
 	GuString str = (*env)->GetStringUTFChars(env, s, 0);
 	GuString copy = gu_string_copy(str, pool);
@@ -64,7 +64,7 @@ j2gu_string(JNIEnv *env, jstring s, GuPool* pool) {
 	return copy;
 }
 
-size_t
+JPGF_INTERNAL size_t
 gu2j_string_offset(GuString s, size_t offset) {
 	const char* utf8 = s;
 	size_t joffset = 0;
@@ -75,7 +75,7 @@ gu2j_string_offset(GuString s, size_t offset) {
 	return joffset;
 }
 
-size_t
+JPGF_INTERNAL size_t
 j2gu_string_offset(GuString s, size_t joffset) {
 	const char* utf8 = s;
 	while (joffset > 0) {
@@ -85,13 +85,13 @@ j2gu_string_offset(GuString s, size_t joffset) {
 	return utf8-s;
 }
 
-void*
+JPGF_INTERNAL void*
 get_ref(JNIEnv *env, jobject self) {
 	jfieldID refId = (*env)->GetFieldID(env, (*env)->GetObjectClass(env, self), "ref", "J");
 	return l2p((*env)->GetLongField(env, self, refId));
 }
 
-void
+JPGF_INTERNAL void
 throw_jstring_exception(JNIEnv *env, const char* class_name, jstring msg)
 {
 	jclass exception_class = (*env)->FindClass(env, class_name);
@@ -106,7 +106,7 @@ throw_jstring_exception(JNIEnv *env, const char* class_name, jstring msg)
 	(*env)->Throw(env, exception);
 }
 
-void
+JPGF_INTERNAL void
 throw_string_exception(JNIEnv *env, const char* class_name, const char* msg)
 {
 	jstring jmsg = (*env)->NewStringUTF(env, msg);
diff --git a/src/runtime/java/jni_utils.h b/src/runtime/java/jni_utils.h
index 4247b99a1..f2d050092 100644
--- a/src/runtime/java/jni_utils.h
+++ b/src/runtime/java/jni_utils.h
@@ -1,31 +1,44 @@
 #ifndef JNI_UTILS
 #define JNI_UTILS
 
+#if defined(_MSC_VER)
+
+#define JPGF_INTERNAL_DECL
+#define JPGF_INTERNAL
+
+#else
+
+#define JPGF_INTERNAL_DECL  __attribute__ ((visibility ("hidden")))
+#define JPGF_INTERNAL       __attribute__ ((visibility ("hidden")))
+
+#endif
+
+
 #define l2p(x) ((void*) (intptr_t) (x))
 #define p2l(x) ((jlong) (intptr_t) (x))
 
-jstring
+JPGF_INTERNAL_DECL jstring
 gu2j_string(JNIEnv *env, GuString s);
 
-jstring
+JPGF_INTERNAL_DECL jstring
 gu2j_string_buf(JNIEnv *env, GuStringBuf* sbuf);
 
-GuString
+JPGF_INTERNAL_DECL GuString
 j2gu_string(JNIEnv *env, jstring s, GuPool* pool);
 
-size_t
+JPGF_INTERNAL_DECL size_t
 gu2j_string_offset(GuString s, size_t offset);
 
-size_t
+JPGF_INTERNAL_DECL size_t
 j2gu_string_offset(GuString s, size_t joffset);
 
-void*
+JPGF_INTERNAL_DECL void*
 get_ref(JNIEnv *env, jobject self);
 
-void
+JPGF_INTERNAL_DECL void
 throw_jstring_exception(JNIEnv *env, const char* class_name, jstring msg);
 
-void
+JPGF_INTERNAL_DECL void
 throw_string_exception(JNIEnv *env, const char* class_name, const char* msg);
 
 #endif