diff --git a/lemon/lgf_reader.h b/lemon/lgf_reader.h
--- a/lemon/lgf_reader.h
+++ b/lemon/lgf_reader.h
@@ -195,44 +195,44 @@
       }
     };
 
-    bool isWhiteSpace(char c) {
+    inline bool isWhiteSpace(char c) {
       return c == ' ' || c == '\t' || c == '\v' || 
         c == '\n' || c == '\r' || c == '\f'; 
     }
     
-    bool isOct(char c) {
+    inline bool isOct(char c) {
       return '0' <= c && c <='7'; 
     }
     
-    int valueOct(char c) {
+    inline int valueOct(char c) {
       LEMON_ASSERT(isOct(c), "The character is not octal.");
       return c - '0';
     }
 
-    bool isHex(char c) {
+    inline bool isHex(char c) {
       return ('0' <= c && c <= '9') || 
 	('a' <= c && c <= 'z') || 
 	('A' <= c && c <= 'Z'); 
     }
     
-    int valueHex(char c) {
+    inline int valueHex(char c) {
       LEMON_ASSERT(isHex(c), "The character is not hexadecimal.");
       if ('0' <= c && c <= '9') return c - '0';
       if ('a' <= c && c <= 'z') return c - 'a' + 10;
       return c - 'A' + 10;
     }
 
-    bool isIdentifierFirstChar(char c) {
+    inline bool isIdentifierFirstChar(char c) {
       return ('a' <= c && c <= 'z') ||
 	('A' <= c && c <= 'Z') || c == '_';
     }
 
-    bool isIdentifierChar(char c) {
+    inline bool isIdentifierChar(char c) {
       return isIdentifierFirstChar(c) ||
 	('0' <= c && c <= '9');
     }
 
-    char readEscape(std::istream& is) {
+    inline char readEscape(std::istream& is) {
       char c;
       if (!is.get(c))
 	throw DataFormatError("Escape format error");
@@ -284,7 +284,7 @@
       } 
     }
     
-    std::istream& readToken(std::istream& is, std::string& str) {
+    inline std::istream& readToken(std::istream& is, std::string& str) {
       std::ostringstream os;
 
       char c;