diff --git a/ext/mysql/libmysql/libmysql.c b/ext/mysql/libmysql/libmysql.c
index e4ddc149520..cd74ceb2a0b 100644
--- a/ext/mysql/libmysql/libmysql.c
+++ b/ext/mysql/libmysql/libmysql.c
@@ -56,7 +56,7 @@ my_string	mysql_unix_port=0;
 #endif
 
 #if defined(MSDOS) || defined(__WIN__)
-// socket_errno is defined in global.h for all platforms
+/* socket_errno is defined in global.h for all platforms */
 #define perror(A)
 #else
 #include <errno.h>
diff --git a/ext/mysql/libmysql/my_getwd.c b/ext/mysql/libmysql/my_getwd.c
index 9b5869e8f0c..0797db25f59 100644
--- a/ext/mysql/libmysql/my_getwd.c
+++ b/ext/mysql/libmysql/my_getwd.c
@@ -19,7 +19,7 @@ This file is public domain and comes with NO WARRANTY of any kind */
 #endif
 
 #ifdef __EMX__
-// chdir2 support also drive change
+/* chdir2 support also drive change */
 #define chdir _chdir2
 #endif
 
diff --git a/ext/mysql/libmysql/my_tempnam.c b/ext/mysql/libmysql/my_tempnam.c
index e90e2553c8b..4a854aea0b0 100644
--- a/ext/mysql/libmysql/my_tempnam.c
+++ b/ext/mysql/libmysql/my_tempnam.c
@@ -85,10 +85,10 @@ my_string my_tempnam(const char *dir, const char *pfx,
     dir=temp;
   }
 #ifdef OS2
-  // changing environ variable doesn't work with VACPP
+  /* changing environ variable doesn't work with VACPP */
   char  buffer[256];
   sprintf( buffer, "TMP=%s", dir);
-  // remove ending backslash
+  /* remove ending backslash */
   if (buffer[strlen(buffer)-1] == '\\')
      buffer[strlen(buffer)-1] = '\0';
   putenv( buffer);