diff --git cpp/src/phonenumbers/encoding_utils.h cpp/src/phonenumbers/encoding_utils.h
index d4271832..0c65d2bf 100644
--- cpp/src/phonenumbers/encoding_utils.h
+++ cpp/src/phonenumbers/encoding_utils.h
@@ -29,7 +29,7 @@ class EncodingUtils {
   // the function stores 0xFFFD in the output variable and returns 1.
   static inline int DecodeUTF8Char(const char* in, char32* out) {
     Rune r;
-    int len = chartorune(&r, in);
+    int len = _chartorune(&r, in);
     *out = r;
     return len;
   }
diff --git cpp/src/phonenumbers/utf/rune.c cpp/src/phonenumbers/utf/rune.c
index b4aa93b5..6f7b0358 100644
--- cpp/src/phonenumbers/utf/rune.c
+++ cpp/src/phonenumbers/utf/rune.c
@@ -64,7 +64,7 @@ enum
  * reasons, we return 1 instead of 0.
  */
 int
-charntorune(Rune *rune, const char *str, int length)
+_charntorune(Rune *rune, const char *str, int length)
 {
 	int c, c1, c2, c3;
 	long l;
@@ -167,7 +167,7 @@ badlen:
  * null-terminated strings.
  */
 int
-chartorune(Rune *rune, const char *str)
+_chartorune(Rune *rune, const char *str)
 {
 	int c, c1, c2, c3;
 	long l;
@@ -247,12 +247,12 @@ bad:
 int
 isvalidcharntorune(const char* str, int length, Rune* rune, int* consumed)
 {
-	*consumed = charntorune(rune, str, length);
+	*consumed = _charntorune(rune, str, length);
 	return *rune != Runeerror || *consumed == 3;
 }
 
 int
-runetochar(char *str, const Rune *rune)
+_runetochar(char *str, const Rune *rune)
 {
 	/* Runes are signed, so convert to unsigned for range check. */
 	unsigned long c;
@@ -311,15 +311,15 @@ runetochar(char *str, const Rune *rune)
 }
 
 int
-runelen(Rune rune)
+_runelen(Rune rune)
 {
 	char str[10];
 
-	return runetochar(str, &rune);
+	return _runetochar(str, &rune);
 }
 
 int
-runenlen(const Rune *r, int nrune)
+_runenlen(const Rune *r, int nrune)
 {
 	int nb, c;
 
@@ -339,7 +339,7 @@ runenlen(const Rune *r, int nrune)
 }
 
 int
-fullrune(const char *str, int n)
+_fullrune(const char *str, int n)
 {
 	if (n > 0) {
 		int c = *(uchar*)str;
diff --git cpp/src/phonenumbers/utf/unicodetext.cc cpp/src/phonenumbers/utf/unicodetext.cc
index 11f68f76..86504a31 100644
--- cpp/src/phonenumbers/utf/unicodetext.cc
+++ cpp/src/phonenumbers/utf/unicodetext.cc
@@ -362,7 +362,7 @@ void UnicodeText::push_back(char32 c) {
   if (UniLib::IsValidCodepoint(c)) {
     char buf[UTFmax];
     Rune rune = c;
-    int len = runetochar(buf, &rune);
+    int len = _runetochar(buf, &rune);
     if (UniLib::IsInterchangeValid(buf, len)) {
       repr_.append(buf, len);
     } else {
diff --git cpp/src/phonenumbers/utf/unilib.cc cpp/src/phonenumbers/utf/unilib.cc
index e890f974..ce549363 100644
--- cpp/src/phonenumbers/utf/unilib.cc
+++ cpp/src/phonenumbers/utf/unilib.cc
@@ -50,7 +50,7 @@ int SpanInterchangeValid(const char* begin, int byte_length) {
   const char* p = begin;
   const char* end = begin + byte_length;
   while (p < end) {
-    int bytes_consumed = charntorune(&rune, p, end - p);
+    int bytes_consumed = _charntorune(&rune, p, end - p);
     // We want to accept Runeerror == U+FFFD as a valid char, but it is used
     // by chartorune to indicate error. Luckily, the real codepoint is size 3
     // while errors return bytes_consumed <= 1.
diff --git cpp/src/phonenumbers/utf/utf.h cpp/src/phonenumbers/utf/utf.h
index 72d01ed6..35fd0ea9 100644
--- cpp/src/phonenumbers/utf/utf.h
+++ cpp/src/phonenumbers/utf/utf.h
@@ -46,7 +46,7 @@ extern "C" {
 // runetochar copies (encodes) one rune, pointed to by r, to at most
 // UTFmax bytes starting at s and returns the number of bytes generated.
 
-int runetochar(char* s, const Rune* r);
+int _runetochar(char* s, const Rune* r);
 
 
 // chartorune copies (decodes) at most UTFmax bytes starting at s to
@@ -59,7 +59,7 @@ int runetochar(char* s, const Rune* r);
 // Unicode value 0 (i.e., ASCII NULL). A byte value of 0 is illegal
 // anywhere else in a UTF sequence.
 
-int chartorune(Rune* r, const char* s);
+int _chartorune(Rune* r, const char* s);
 
 
 // charntorune is like chartorune, except that it will access at most
@@ -69,7 +69,7 @@ int chartorune(Rune* r, const char* s);
 //
 // Added 2004-09-24 by Wei-Hwa Huang
 
-int charntorune(Rune* r, const char* s, int n);
+int _charntorune(Rune* r, const char* s, int n);
 
 // isvalidcharntorune(str, n, r, consumed)
 // is a convenience function that calls "*consumed = charntorune(r, str, n)"
@@ -80,13 +80,13 @@ int isvalidcharntorune(const char* str, int n, Rune* r, int* consumed);
 
 // runelen returns the number of bytes required to convert r into UTF.
 
-int runelen(Rune r);
+int _runelen(Rune r);
 
 
 // runenlen returns the number of bytes required to convert the n
 // runes pointed to by r into UTF.
 
-int runenlen(const Rune* r, int n);
+int _runenlen(const Rune* r, int n);
 
 
 // fullrune returns 1 if the string s of length n is long enough to be
@@ -95,7 +95,7 @@ int runenlen(const Rune* r, int n);
 // by programs that obtain input one byte at a time and need to know
 // when a full rune has arrived.
 
-int fullrune(const char* s, int n);
+int _fullrune(const char* s, int n);
 
 // The following routines are analogous to the corresponding string
 // routines with "utf" substituted for "str", and "rune" substituted