diff --git a/include/xlsxwriter/third_party/ioapi.h b/include/xlsxwriter/third_party/ioapi.h
index c79aa1e6..32bae47a 100644
--- a/include/xlsxwriter/third_party/ioapi.h
+++ b/include/xlsxwriter/third_party/ioapi.h
@@ -29,8 +29,8 @@
 
 #if (!defined(_WIN32)) && (!defined(WIN32)) && (!defined(__APPLE__))
 
-  // Linux needs this to support file operation on files larger then 4+GB
-  // But might need better if/def to select just the platforms that needs them.
+  /* Linux needs this to support file operation on files larger then 4+GB
+   * But might need better if/def to select just the platforms that needs them. */
 
         #ifndef __USE_FILE_OFFSET64
                 #define __USE_FILE_OFFSET64
@@ -66,7 +66,7 @@
  #if (_MSC_VER >= 1400) && (!(defined(NO_MSCVER_FILE64_FUNC)))
   #define ftello64 _ftelli64
   #define fseeko64 _fseeki64
- #else // old MSC
+ #else /* old MSC */
   #define ftello64 ftell
   #define fseeko64 fseek
  #endif
@@ -194,8 +194,8 @@ typedef struct zlib_filefunc64_32_def_s
 
 #define ZREAD64(filefunc,filestream,buf,size)     ((*((filefunc).zfile_func64.zread_file))   ((filefunc).zfile_func64.opaque,filestream,buf,size))
 #define ZWRITE64(filefunc,filestream,buf,size)    ((*((filefunc).zfile_func64.zwrite_file))  ((filefunc).zfile_func64.opaque,filestream,buf,size))
-//#define ZTELL64(filefunc,filestream)            ((*((filefunc).ztell64_file)) ((filefunc).opaque,filestream))
-//#define ZSEEK64(filefunc,filestream,pos,mode)   ((*((filefunc).zseek64_file)) ((filefunc).opaque,filestream,pos,mode))
+/* #define ZTELL64(filefunc,filestream)            ((*((filefunc).ztell64_file)) ((filefunc).opaque,filestream)) */
+/* #define ZSEEK64(filefunc,filestream,pos,mode)   ((*((filefunc).zseek64_file)) ((filefunc).opaque,filestream,pos,mode)) */
 #define ZCLOSE64(filefunc,filestream)             ((*((filefunc).zfile_func64.zclose_file))  ((filefunc).zfile_func64.opaque,filestream))
 #define ZERROR64(filefunc,filestream)             ((*((filefunc).zfile_func64.zerror_file))  ((filefunc).zfile_func64.opaque,filestream))
 
diff --git a/include/xlsxwriter/third_party/zip.h b/include/xlsxwriter/third_party/zip.h
index efe63142..19213394 100644
--- a/include/xlsxwriter/third_party/zip.h
+++ b/include/xlsxwriter/third_party/zip.h
@@ -49,7 +49,7 @@
 extern "C" {
 #endif
 
-//#define HAVE_BZIP2
+/* #define HAVE_BZIP2 */
 
 #ifndef _ZLIB_H
 #include "zlib.h"
diff --git a/third_party/minizip/ioapi.h b/third_party/minizip/ioapi.h
index c79aa1e6..32bae47a 100644
--- a/third_party/minizip/ioapi.h
+++ b/third_party/minizip/ioapi.h
@@ -29,8 +29,8 @@
 
 #if (!defined(_WIN32)) && (!defined(WIN32)) && (!defined(__APPLE__))
 
-  // Linux needs this to support file operation on files larger then 4+GB
-  // But might need better if/def to select just the platforms that needs them.
+  /* Linux needs this to support file operation on files larger then 4+GB
+   * But might need better if/def to select just the platforms that needs them. */
 
         #ifndef __USE_FILE_OFFSET64
                 #define __USE_FILE_OFFSET64
@@ -66,7 +66,7 @@
  #if (_MSC_VER >= 1400) && (!(defined(NO_MSCVER_FILE64_FUNC)))
   #define ftello64 _ftelli64
   #define fseeko64 _fseeki64
- #else // old MSC
+ #else /* old MSC */
   #define ftello64 ftell
   #define fseeko64 fseek
  #endif
@@ -194,8 +194,8 @@ typedef struct zlib_filefunc64_32_def_s
 
 #define ZREAD64(filefunc,filestream,buf,size)     ((*((filefunc).zfile_func64.zread_file))   ((filefunc).zfile_func64.opaque,filestream,buf,size))
 #define ZWRITE64(filefunc,filestream,buf,size)    ((*((filefunc).zfile_func64.zwrite_file))  ((filefunc).zfile_func64.opaque,filestream,buf,size))
-//#define ZTELL64(filefunc,filestream)            ((*((filefunc).ztell64_file)) ((filefunc).opaque,filestream))
-//#define ZSEEK64(filefunc,filestream,pos,mode)   ((*((filefunc).zseek64_file)) ((filefunc).opaque,filestream,pos,mode))
+/* #define ZTELL64(filefunc,filestream)            ((*((filefunc).ztell64_file)) ((filefunc).opaque,filestream)) */
+/* #define ZSEEK64(filefunc,filestream,pos,mode)   ((*((filefunc).zseek64_file)) ((filefunc).opaque,filestream,pos,mode)) */
 #define ZCLOSE64(filefunc,filestream)             ((*((filefunc).zfile_func64.zclose_file))  ((filefunc).zfile_func64.opaque,filestream))
 #define ZERROR64(filefunc,filestream)             ((*((filefunc).zfile_func64.zerror_file))  ((filefunc).zfile_func64.opaque,filestream))
 
diff --git a/third_party/minizip/zip.h b/third_party/minizip/zip.h
index efe63142..19213394 100644
--- a/third_party/minizip/zip.h
+++ b/third_party/minizip/zip.h
@@ -49,7 +49,7 @@
 extern "C" {
 #endif
 
-//#define HAVE_BZIP2
+/* #define HAVE_BZIP2 */
 
 #ifndef _ZLIB_H
 #include "zlib.h"