diff --git a/api/boinc_api.h b/api/boinc_api.h
index 0471a74bf5..740479aae6 100755
--- a/api/boinc_api.h
+++ b/api/boinc_api.h
@@ -22,8 +22,12 @@
 
 /* to allow prototypes using 'bool' in ANSI-C */
 #if (!defined __cplusplus) && (!defined bool)
-#  define bool int
-#endif
+#if ((defined(_MSC_VER)) && (_MSC_VER > 1020))
+#define bool char
+#else
+#define bool int
+#endif /* defined(_MSC_VER) && (_MSC_VER > 1020) */
+#endif /* (!defined __cplusplus) && (!defined bool) */
 
 /* ----------------------------------------------------------------------
  * ANSI C API BEGINS HERE
diff --git a/api/graphics_api.h b/api/graphics_api.h
index a03339c428..351243bd7d 100755
--- a/api/graphics_api.h
+++ b/api/graphics_api.h
@@ -6,8 +6,12 @@
  */
 /* to allow prototypes using 'bool' in ANSI-C */
 #if (!defined __cplusplus) && (!defined bool)
-#  define bool int
-#endif
+#if ((defined(_MSC_VER)) && (_MSC_VER > 1020))
+#define bool char
+#else
+#define bool int
+#endif /* defined(_MSC_VER) && (_MSC_VER > 1020) */
+#endif /* (!defined __cplusplus) && (!defined bool) */
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/checkin_notes b/checkin_notes
index 4c511c66f1..7f0081514f 100755
--- a/checkin_notes
+++ b/checkin_notes
@@ -20732,3 +20732,23 @@ David  5 Dec 2004
         boinc_db.h
     lib/
         util.C,h
+
+Bruce 6 Dec 2004 [thanks to Bernd Machenschalk!]
+
+    - Fixed 'time to checkpoint' problem under Win32 with pure C code.
+      It turns out that MS VC++ up to version 4.2 defines bool as INT.
+      But more recent VC++ defines bool as CHAR.  This broke
+      boinc_time_to_checkpoint() under Win32, when used within pure ANSI
+      C code, if you treated the return value as a bool. So this patch
+      defines bool as char if using C under recent MS compilers.
+
+      David, a better solution for API functions that should be
+      callable from C is to make them return 'int' not 'bool'.
+      Probably ditto for Fortran. Sigh.
+
+    api/
+    boinc_api.h
+    graphics_api.h
+
+    lib/
+        filesys.h
diff --git a/lib/filesys.h b/lib/filesys.h
index 5e159f839c..4a2cde8eb5 100755
--- a/lib/filesys.h
+++ b/lib/filesys.h
@@ -26,11 +26,16 @@
 #ifndef _FILESYS_
 #define _FILESYS_
 
-/* to allow prototypes using 'bool' in ANSI-C */
+/* to allow prototypes using 'bool' in ANSI-C.  Note that gcc defines
+   bool as an INT, and MS VC++ up to version 4.2 also does.  However
+   more recent versions of MS VC++ define bool as CHAR.  */
 #if (!defined __cplusplus) && (!defined bool)
-#  define bool int
-#endif
-
+#if ((defined(_MSC_VER)) && (_MSC_VER > 1020))
+#define bool char
+#else
+#define bool int
+#endif /* defined(_MSC_VER) && (_MSC_VER > 1020) */
+#endif /* (!defined __cplusplus) && (!defined bool) */
 
 #ifdef _WIN32