diff --git a/lib/mprintf.c b/lib/mprintf.c
index 25a4196ae..475bdded5 100644
--- a/lib/mprintf.c
+++ b/lib/mprintf.c
@@ -409,7 +409,7 @@ static long dprintf_Pass1(const char *format, va_stack_t *vto, char **endpos,
 #endif
           break;
         case 'O':
-#if SIZEOF_CURL_OFF_T > 4
+#if CURL_SIZEOF_CURL_OFF_T > 4
           flags |= FLAGS_LONGLONG;
 #else
           flags |= FLAGS_LONG;
diff --git a/lib/progress.c b/lib/progress.c
index 2956d1a99..b0aa853f0 100644
--- a/lib/progress.c
+++ b/lib/progress.c
@@ -86,7 +86,7 @@ static char *max5data(curl_off_t bytes, char *max5)
              (int)(bytes/ONE_MEGABYTE),
              (int)(bytes%ONE_MEGABYTE)/(ONE_MEGABYTE/10) );
   }
-#if SIZEOF_CURL_OFF_T > 4
+#if CURL_SIZEOF_CURL_OFF_T > 4
   else if(bytes < ( (curl_off_t)10000*ONE_MEGABYTE))
     /* 'XXXXM' is good until we're at 10000MB or above */
     snprintf(max5, 6, "%4" FORMAT_OFF_T "M", (curl_off_t)(bytes/ONE_MEGABYTE));
diff --git a/lib/setup.h b/lib/setup.h
index d43ae85a0..7ccfa66b5 100644
--- a/lib/setup.h
+++ b/lib/setup.h
@@ -112,14 +112,12 @@
 #include <curl/curlrules.h>
 
 /*
- * Set up internal curl_off_t size macro
+ * Ensure that no one is using the old SIZEOF_CURL_OFF_T macro
  */
 
 #ifdef SIZEOF_CURL_OFF_T
-#  error "SIZEOF_CURL_OFF_T shall not be defined before this point!"
-   Error Compilation_aborted_SIZEOF_CURL_OFF_T_already_defined
-#else
-#  define SIZEOF_CURL_OFF_T CURL_SIZEOF_CURL_OFF_T
+#  error "SIZEOF_CURL_OFF_T shall not be defined!"
+   Error Compilation_aborted_SIZEOF_CURL_OFF_T_shall_not_be_defined
 #endif
 
 /*
@@ -284,7 +282,7 @@
 
 
 /* To make large file support transparent even on Windows */
-#if defined(WIN32) && (SIZEOF_CURL_OFF_T > 4)
+#if defined(WIN32) && (CURL_SIZEOF_CURL_OFF_T > 4)
 #include <sys/stat.h>   /* must come first before we redefine stat() */
 #include <io.h>
 #define lseek(x,y,z) _lseeki64(x, y, z)
diff --git a/lib/strtoofft.h b/lib/strtoofft.h
index b53d1cb52..a63dfcbb4 100644
--- a/lib/strtoofft.h
+++ b/lib/strtoofft.h
@@ -38,7 +38,7 @@
  * not, should try to emulate its functionality.  At any rate, we define
  * 'strtoofft' such that it can be used to work with curl_off_t's regardless.
  */
-#if (SIZEOF_CURL_OFF_T > 4) && (SIZEOF_LONG < 8)
+#if (CURL_SIZEOF_CURL_OFF_T > 4) && (SIZEOF_LONG < 8)
 #ifdef HAVE_STRTOLL
 #define curlx_strtoofft strtoll
 #else /* HAVE_STRTOLL */
@@ -54,7 +54,7 @@ curl_off_t curlx_strtoll(const char *nptr, char **endptr, int base);
 #endif /* MSVC7 or later */
 
 #endif /* HAVE_STRTOLL */
-#else /* (SIZEOF_CURL_OFF_T > 4) && (SIZEOF_LONG < 8) */
+#else /* (CURL_SIZEOF_CURL_OFF_T > 4) && (SIZEOF_LONG < 8) */
 /* simply use strtol() to get numbers, either 32 or 64 bit */
 #define curlx_strtoofft strtol
 #endif
diff --git a/lib/version.c b/lib/version.c
index 5fb57525a..a2828ceae 100644
--- a/lib/version.c
+++ b/lib/version.c
@@ -190,7 +190,7 @@ static curl_version_info_data version_info = {
 #ifdef HAVE_SPNEGO
   | CURL_VERSION_SPNEGO
 #endif
-#if defined(ENABLE_64BIT) && (SIZEOF_CURL_OFF_T > 4)
+#if defined(ENABLE_64BIT) && (CURL_SIZEOF_CURL_OFF_T > 4)
   | CURL_VERSION_LARGEFILE
 #endif
 #if defined(CURL_DOES_CONVERSIONS)
diff --git a/src/main.c b/src/main.c
index ceee05bdd..5b6fef738 100644
--- a/src/main.c
+++ b/src/main.c
@@ -212,7 +212,7 @@ typedef enum {
 
 /* Support uploading and resuming of >2GB files
  */
-#if defined(WIN32) && (SIZEOF_CURL_OFF_T > 4)
+#if defined(WIN32) && (CURL_SIZEOF_CURL_OFF_T > 4)
 #define lseek(x,y,z) _lseeki64(x, y, z)
 #define struct_stat struct _stati64
 #define stat(file,st) _stati64(file,st)
@@ -1387,7 +1387,7 @@ static int str2num(long *val, const char *str)
  */
 static int str2offset(curl_off_t *val, const char *str)
 {
-#if SIZEOF_CURL_OFF_T > 4
+#if CURL_SIZEOF_CURL_OFF_T > 4
   /* Ugly, but without going through a bunch of rigmarole, we don't have the
    * definitions for LLONG_{MIN,MAX} or LONG_LONG_{MIN,MAX}.
    */
@@ -3214,7 +3214,7 @@ static int my_seek(void *stream, curl_off_t offset, int whence)
 {
   struct InStruct *in=(struct InStruct *)stream;
 
-#if (SIZEOF_CURL_OFF_T > SIZEOF_OFF_T) && !defined(lseek)
+#if (CURL_SIZEOF_CURL_OFF_T > SIZEOF_OFF_T) && !defined(lseek)
   /* The sizeof check following here is only interesting if curl_off_t is
      larger than off_t, but also not on windows-like systems for which lseek
      is a defined macro that works around the 32bit off_t-problem and thus do