diff --git a/src/internal/libc.h b/src/internal/libc.h
index 703d9853c06f8148bd596358f823d83153c2b078..5ab4e679906e85c3a77dd6483a43ab733511a7d5 100644
--- a/src/internal/libc.h
+++ b/src/internal/libc.h
@@ -46,10 +46,10 @@ extern struct __libc *__libc_loc(void) __attribute__((const));
 
 
 /* Designed to avoid any overhead in non-threaded processes */
-void __lock(volatile int *);
-void __unlock(volatile int *);
-int __lockfile(FILE *);
-void __unlockfile(FILE *);
+void __lock(volatile int *) ATTR_LIBC_VISIBILITY;
+void __unlock(volatile int *) ATTR_LIBC_VISIBILITY;
+int __lockfile(FILE *) ATTR_LIBC_VISIBILITY;
+void __unlockfile(FILE *) ATTR_LIBC_VISIBILITY;
 #define LOCK(x) (libc.threads_minus_1 ? (__lock(x),1) : ((void)(x),1))
 #define UNLOCK(x) (libc.threads_minus_1 ? (__unlock(x),1) : ((void)(x),1))
 
diff --git a/src/internal/stdio_impl.h b/src/internal/stdio_impl.h
index 279e91fdecb975604e25a11bac17d23f84588a6e..80646f8c731398c94a6aaa4ac1beeff569a94aa3 100644
--- a/src/internal/stdio_impl.h
+++ b/src/internal/stdio_impl.h
@@ -74,10 +74,10 @@ size_t __string_read(FILE *, unsigned char *, size_t);
 int __toread(FILE *);
 int __towrite(FILE *);
 
-int __overflow(FILE *, int);
-int __oflow(FILE *);
-int __uflow(FILE *);
-int __underflow(FILE *);
+#if defined(__PIC__) && (100*__GNUC__+__GNUC_MINOR__ >= 303)
+__attribute__((visibility("protected")))
+#endif
+int __overflow(FILE *, int), __uflow(FILE *);
 
 int __fseeko(FILE *, off_t, int);
 int __fseeko_unlocked(FILE *, off_t, int);
diff --git a/src/internal/syscall.h b/src/internal/syscall.h
index 50409ef8168db07e6ef458fefb0ec2b553797bbc..7381efea8d4d1e235d69909074645fca50d3e61e 100644
--- a/src/internal/syscall.h
+++ b/src/internal/syscall.h
@@ -1,9 +1,11 @@
 #ifndef _INTERNAL_SYSCALL_H
 #define _INTERNAL_SYSCALL_H
 
-long __syscall_ret(unsigned long);
-long __syscall(long, ...);
-long __syscall_cp(long, long, long, long, long, long, long);
+#if defined(__PIC__) && (100*__GNUC__+__GNUC_MINOR__ >= 303)
+__attribute__((visibility("protected")))
+#endif
+long __syscall_ret(unsigned long), __syscall(long, ...),
+	__syscall_cp(long, long, long, long, long, long, long);
 
 #include <sys/syscall.h>
 #include "syscall_arch.h"