diff --git a/include/curl/curlbuild.h.dist b/include/curl/curlbuild.h.dist
index 7dd26a6981710df59aae50e2a239bb6d1872dd62..483e69e4ef851ca361427f5c524c12ae2c7e07fb 100644
--- a/include/curl/curlbuild.h.dist
+++ b/include/curl/curlbuild.h.dist
@@ -346,8 +346,12 @@
 
 #elif defined(__MVS__)
 #  if defined(__IBMC__) || defined(__IBMCPP__)
-#    if defined(_LONG_LONG)
+#    if defined(_ILP32)
 #      define CURL_SIZEOF_LONG        4
+#    elif defined(_LP64)
+#      define CURL_SIZEOF_LONG        8
+#    endif
+#    if defined(_LONG_LONG)
 #      define CURL_OFF_T              long long
 #      define CURL_FMT_OFF_T          "lld"
 #      define CURL_FMT_OFF_TU         "llu"
@@ -356,7 +360,6 @@
 #      define CURL_SUFFIX_CURL_OFF_T  LL
 #      define CURL_SUFFIX_CURL_OFF_TU ULL
 #    elif defined(_LP64)
-#      define CURL_SIZEOF_LONG        4
 #      define CURL_OFF_T              long
 #      define CURL_FMT_OFF_T          "ld"
 #      define CURL_FMT_OFF_TU         "lu"
@@ -365,7 +368,6 @@
 #      define CURL_SUFFIX_CURL_OFF_T  L
 #      define CURL_SUFFIX_CURL_OFF_TU UL
 #    else
-#      define CURL_SIZEOF_LONG        4
 #      define CURL_OFF_T              long
 #      define CURL_FMT_OFF_T          "ld"
 #      define CURL_FMT_OFF_TU         "lu"
@@ -378,8 +380,12 @@
 
 #elif defined(__370__)
 #  if defined(__IBMC__) || defined(__IBMCPP__)
-#    if defined(_LONG_LONG)
+#    if defined(_ILP32)
 #      define CURL_SIZEOF_LONG        4
+#    elif defined(_LP64)
+#      define CURL_SIZEOF_LONG        8
+#    endif
+#    if defined(_LONG_LONG)
 #      define CURL_OFF_T              long long
 #      define CURL_FMT_OFF_T          "lld"
 #      define CURL_FMT_OFF_TU         "llu"
@@ -388,7 +394,6 @@
 #      define CURL_SUFFIX_CURL_OFF_T  LL
 #      define CURL_SUFFIX_CURL_OFF_TU ULL
 #    elif defined(_LP64)
-#      define CURL_SIZEOF_LONG        4
 #      define CURL_OFF_T              long
 #      define CURL_FMT_OFF_T          "ld"
 #      define CURL_FMT_OFF_TU         "lu"
@@ -397,7 +402,6 @@
 #      define CURL_SUFFIX_CURL_OFF_T  L
 #      define CURL_SUFFIX_CURL_OFF_TU UL
 #    else
-#      define CURL_SIZEOF_LONG        4
 #      define CURL_OFF_T              long
 #      define CURL_FMT_OFF_T          "ld"
 #      define CURL_FMT_OFF_TU         "lu"