Index: flang/module/iso_c_binding.f90
===================================================================
--- flang/module/iso_c_binding.f90
+++ flang/module/iso_c_binding.f90
@@ -21,7 +21,8 @@
   type(c_funptr), parameter :: c_null_funptr = c_funptr(0)
 
   ! Table 18.2 (in clause 18.3.1)
-  ! TODO: Specialize (via macros?) for alternative targets
+  ! The following C types (c_int8_t .. c_intmax_t) are defined in stdint.h on
+  ! linux (/usr/include/stdint.h).
   integer, parameter :: &
     c_int8_t = 1, &
     c_int16_t = 2, &
@@ -35,20 +36,29 @@
     c_long_long = c_int64_t, &
     c_signed_char = c_int8_t, &
     c_size_t = kind(c_sizeof(1)), &
-    c_intmax_t = c_int128_t, &
+    c_intmax_t = c_int64_t, & ! Is c_int128_t if it is supported in future
     c_intptr_t = c_size_t, &
     c_ptrdiff_t = c_size_t
   integer, parameter :: &
     c_int_least8_t = c_int8_t, &
-    c_int_fast8_t = c_int8_t, &
     c_int_least16_t = c_int16_t, &
-    c_int_fast16_t = c_int16_t, &
     c_int_least32_t = c_int32_t, &
-    c_int_fast32_t = c_int32_t, &
     c_int_least64_t = c_int64_t, &
-    c_int_fast64_t = c_int64_t, &
     c_int_least128_t = c_int128_t, &
     c_int_fast128_t = c_int128_t
+#if defined(_WIN32) || defined(__MACH__)
+  integer, parameter :: &
+    c_int_fast8_t = c_int8_t, &
+    c_int_fast16_t = c_int16_t, &
+    c_int_fast32_t = c_int32_t, &
+    c_int_fast64_t = c_int64_t
+#else
+  integer, parameter :: &
+    c_int_fast8_t = c_int8_t, &
+    c_int_fast16_t = c_int64_t, &
+    c_int_fast32_t = c_int64_t, &
+    c_int_fast64_t = c_int64_t
+#endif
 
   integer, parameter :: &
     c_float = 4, &