diff --git a/Source/build.cpp b/Source/build.cpp
index 0490e0d0..cc15e245 100644
--- a/Source/build.cpp
+++ b/Source/build.cpp
@@ -8,6 +8,7 @@
 #include "util.h"
 #include "fileform.h"
 #include "writer.h"
+#include "crc32.h"
 
 #include <stdexcept>
 
@@ -2274,7 +2275,7 @@ int CEXEBuild::write_output(void)
 
   RET_UNLESS_OK( uninstall_generate() );
 
-  int crc=0;
+  crc32_t crc=0;
 
   {
     string full_path = get_full_path(build_output_filename);
@@ -2349,7 +2350,7 @@ int CEXEBuild::write_output(void)
     }
 
     if (!build_compress_whole)
-      fh.length_of_all_following_data=ihd.getlen()+build_datablock.getlen()+(int)sizeof(firstheader)+(build_crcchk?sizeof(int):0);
+      fh.length_of_all_following_data=ihd.getlen()+build_datablock.getlen()+(int)sizeof(firstheader)+(build_crcchk?sizeof(crc32_t):0);
     else
       fd_start=ftell(fp);
 
@@ -2384,7 +2385,7 @@ int CEXEBuild::write_output(void)
         return PS_ERROR;
       }
 #ifdef NSIS_CONFIG_CRC_SUPPORT
-      crc_writer_sink crc_sink((unsigned long *) &crc);
+      crc_writer_sink crc_sink((crc32_t *) &crc);
       firstheader_writer w(&crc_sink);
       w.write(&fh);
 
@@ -2455,7 +2456,7 @@ int CEXEBuild::write_output(void)
   if (db_opt_save)
   {
     int total_out_size_estimate=
-      m_exehead_size+sizeof(fh)+build_datablock.getlen()+(build_crcchk?sizeof(int):0);
+      m_exehead_size+sizeof(fh)+build_datablock.getlen()+(build_crcchk?sizeof(crc32_t):0);
 #ifdef _WIN32
     int pc=MulDiv(db_opt_save,1000,db_opt_save+total_out_size_estimate);
 #else
@@ -2564,7 +2565,7 @@ int CEXEBuild::write_output(void)
 
     unsigned fend = ftell(fp);
 
-    fh.length_of_all_following_data=ftell(fp)-fd_start+(build_crcchk?sizeof(int):0);
+    fh.length_of_all_following_data=ftell(fp)-fd_start+(build_crcchk?sizeof(crc32_t):0);
     INFO_MSG(
       "%10d / %d bytes\n",
       ftell(fp) - fd_start,
@@ -2608,9 +2609,9 @@ int CEXEBuild::write_output(void)
   {
     total_usize+=sizeof(int);
     int rcrc = FIX_ENDIAN_INT32(crc);
-    if (fwrite(&rcrc,1,sizeof(int),fp) != sizeof(int))
+    if (fwrite(&rcrc,1,sizeof(crc32_t),fp) != sizeof(crc32_t))
     {
-      ERROR_MSG("Error: can't write %d bytes to output\n",sizeof(int));
+      ERROR_MSG("Error: can't write %d bytes to output\n",sizeof(crc32_t));
       fclose(fp);
       return PS_ERROR;
     }
@@ -2693,7 +2694,7 @@ int CEXEBuild::uninstall_generate()
       if (err < 0) return PS_ERROR;
     }
 
-    int crc=0;
+    crc32_t crc=0;
 
     // Get offsets of icons to replace for uninstall
     // Also makes sure that the icons are there and in the right size.
@@ -2763,7 +2764,7 @@ int CEXEBuild::uninstall_generate()
 #endif
     fh.siginfo=FH_SIG;
     fh.length_of_all_following_data=
-      uhd.getlen()+ubuild_datablock.getlen()+(int)sizeof(firstheader)+(build_crcchk?sizeof(int):0);
+      uhd.getlen()+ubuild_datablock.getlen()+(int)sizeof(firstheader)+(build_crcchk?sizeof(crc32_t):0);
 
     MMapBuf udata;
 
@@ -2832,7 +2833,7 @@ int CEXEBuild::uninstall_generate()
       }
 
       firstheader *_fh=(firstheader *)udata.get(0, sizeof(firstheader));
-      _fh->length_of_all_following_data=FIX_ENDIAN_INT32(udata.getlen()+(build_crcchk?sizeof(int):0));
+      _fh->length_of_all_following_data=FIX_ENDIAN_INT32(udata.getlen()+(build_crcchk?sizeof(crc32_t):0));
       udata.release();
     }
     else
diff --git a/Source/build.h b/Source/build.h
index 2307ce57..5434935a 100644
--- a/Source/build.h
+++ b/Source/build.h
@@ -35,13 +35,6 @@
 #  include "Plugins.h"
 #endif //NSIS_CONFIG_PLUGIN_SUPPORT
 
-#ifdef NSIS_CONFIG_CRC_SUPPORT
-extern "C"
-{
-  unsigned long NSISCALL CRC32(unsigned long crc, const unsigned char *buf, unsigned int len);
-};
-#endif
-
 #define PS_OK 0
 #define PS_EOF 1
 #define PS_ERROR 50
diff --git a/Source/crc32.c b/Source/crc32.c
index 781c127e..eed0c883 100644
--- a/Source/crc32.c
+++ b/Source/crc32.c
@@ -1,20 +1,21 @@
 #include "Platform.h"
+#include "crc32.h"
 #include "exehead/config.h"
 #ifdef NSIS_CONFIG_CRC_SUPPORT
 
 // this is based on the (slow,small) CRC32 implementation from zlib.
-unsigned long NSISCALL CRC32(unsigned long crc, const unsigned char *buf, unsigned int len)
+crc32_t NSISCALL CRC32(crc32_t crc, const unsigned char *buf, unsigned int len)
 {
-    static unsigned long crc_table[256];
+    static crc32_t crc_table[256];
 
     if (!crc_table[1])
     {
-      unsigned long c;
+      crc32_t c;
       int n, k;
 
       for (n = 0; n < 256; n++)
       {
-        c = (unsigned long)n;
+        c = (crc32_t)n;
         for (k = 0; k < 8; k++) c = (c >> 1) ^ (c & 1 ? 0xedb88320L : 0);
         crc_table[n] = c;
       }
diff --git a/Source/crc32.h b/Source/crc32.h
new file mode 100644
index 00000000..d40a132a
--- /dev/null
+++ b/Source/crc32.h
@@ -0,0 +1,13 @@
+#include "Platform.h"
+
+#ifndef ___CRC32__H___
+#define ___CRC32__H___
+
+typedef UINT32 crc32_t;
+
+#ifdef __cplusplus
+extern "C"
+#endif
+crc32_t NSISCALL CRC32(crc32_t crc, const unsigned char *buf, unsigned int len);
+
+#endif//!___CRC32__H___
diff --git a/Source/exehead/fileform.c b/Source/exehead/fileform.c
index 739a636b..fd833ffb 100644
--- a/Source/exehead/fileform.c
+++ b/Source/exehead/fileform.c
@@ -6,6 +6,7 @@
 #include "lang.h"
 #include "ui.h"
 #include "exec.h"
+#include "../crc32.h"
 
 #ifdef NSIS_CONFIG_COMPRESSION_SUPPORT
 #ifdef NSIS_COMPRESS_USE_ZLIB
@@ -95,8 +96,6 @@ BOOL CALLBACK verProc(HWND hwndDlg, UINT uMsg, WPARAM wParam, LPARAM lParam)
 static z_stream g_inflate_stream;
 #endif
 
-extern unsigned long NSISCALL CRC32(unsigned long crc, const unsigned char *buf, unsigned int len);
-
 const char * NSISCALL loadHeaders(int cl_flags)
 {
 #ifdef NSIS_CONFIG_CRC_SUPPORT
@@ -104,7 +103,7 @@ const char * NSISCALL loadHeaders(int cl_flags)
   HWND hwnd = 0;
   unsigned int verify_time = GetTickCount() + 1000;
 #endif
-  int crc = 0;
+  crc32_t crc = 0;
   int do_crc = 0;
 #endif//NSIS_CONFIG_CRC_SUPPORT
   int left;
@@ -230,9 +229,9 @@ const char * NSISCALL loadHeaders(int cl_flags)
 #ifdef NSIS_CONFIG_CRC_SUPPORT
   if (do_crc)
   {
-    int fcrc;
+    crc32_t fcrc;
     SetSelfFilePointer(m_pos);
-    if (!ReadSelfFile(&fcrc, sizeof(int)) || crc != fcrc)
+    if (!ReadSelfFile(&fcrc, sizeof(crc32_t)) || crc != fcrc)
       return _LANG_INVALIDCRC;
   }
 #endif//NSIS_CONFIG_CRC_SUPPORT
@@ -251,7 +250,7 @@ const char * NSISCALL loadHeaders(int cl_flags)
   }
   dbd_srcpos = SetSelfFilePointer(g_filehdrsize + sizeof(firstheader));
 #ifdef NSIS_CONFIG_CRC_SUPPORT
-  dbd_fulllen = dbd_srcpos - sizeof(h) + h.length_of_all_following_data - ((h.flags & FH_FLAGS_NO_CRC) ? 0 : sizeof(int));
+  dbd_fulllen = dbd_srcpos - sizeof(h) + h.length_of_all_following_data - ((h.flags & FH_FLAGS_NO_CRC) ? 0 : sizeof(crc32_t));
 #else
   dbd_fulllen = dbd_srcpos - sizeof(h) + h.length_of_all_following_data;
 #endif//NSIS_CONFIG_CRC_SUPPORT
diff --git a/Source/writer.cpp b/Source/writer.cpp
index 491885ee..1ef240e9 100644
--- a/Source/writer.cpp
+++ b/Source/writer.cpp
@@ -64,7 +64,7 @@ void file_writer_sink::write_data(const void *data, const size_t size)
 }
 
 #ifdef NSIS_CONFIG_CRC_SUPPORT
-extern "C" unsigned long NSISCALL CRC32(unsigned long crc, const unsigned char *buf, unsigned int len);
+#include "crc32.h"
 
 void crc_writer_sink::write_data(const void *data, const size_t size)
 {
diff --git a/Source/writer.h b/Source/writer.h
index 56ab7adc..f7caf8db 100644
--- a/Source/writer.h
+++ b/Source/writer.h
@@ -3,6 +3,7 @@
 
 #include "exehead/config.h"
 #include "growbuf.h"
+#include "crc32.h"
 #include <stdio.h>
 
 class writer_sink {
@@ -57,12 +58,12 @@ private:
 #ifdef NSIS_CONFIG_CRC_SUPPORT
 class crc_writer_sink : public writer_sink {
 public:
-  crc_writer_sink(unsigned long *crc) : m_crc(crc) {}
+  crc_writer_sink(crc32_t *crc) : m_crc(crc) {}
 
   virtual void write_data(const void *data, const size_t size);
 
 private:
-  unsigned long *m_crc;
+  crc32_t *m_crc;
 
 };
 #endif