diff --git a/sim_printf_fmts.h b/sim_printf_fmts.h
index e31389381..e208cf958 100644
--- a/sim_printf_fmts.h
+++ b/sim_printf_fmts.h
@@ -5,6 +5,7 @@
  * this header so that these formats are available to more than SCP.
  *
  * Author: B. Scott Michel
+ *         C. Gauger-Cosgrove
  *
  * "scooter me fecit"
  *~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~*/
@@ -15,7 +16,9 @@
 /* cross-platform printf() format specifiers:
  *
  * Note: MS apparently does recognize "ll" as "l" in its printf() routines, but "I64" is
- * preferred for 64-bit types.
+ * preferred for 64-bit types.  _MSC_VER and _WIN32 are always defined for Visual Studio
+ * builds. To check if the build is using 64-bit Visual Studio, you must check if the
+ * _WIN64 macro is defined.
  *
  * MinGW note: __MINGW64__ and __MINGW32__ are both defined by 64-bit gcc. Check
  * for __MINGW64__ before __MINGW32__.
@@ -29,22 +32,26 @@
  * POINTER_FMT: Format modifier for pointers, e.g. "%08" POINTER_FMT "X"
 */
 
-#if defined (_WIN32) || defined(_WIN64)
-
-#  if defined(__MINGW64__)
-#    define LL_FMT     "I64"
-#    define SIZE_T_FMT "I64"
-#  elif defined(_MSC_VER) || defined(__MINGW32__)
-#    define LL_FMT     "ll"
-#    define SIZE_T_FMT "z"
-#  else
-     /* Graceful fail -- shouldn't ever default to this on a Windows platform. */
-#    define LL_FMT     "ll"
-#    define SIZE_T_FMT "I32"
+#if defined(_MSC_VER) || defined(__MINGW32__) || defined(__MINGW64__)
+#  if _MSC_VER >= 1900 || defined(__USE_MINGW_ANSI_STDIO)
+/* VS 2015 or later, MinGW with ANSI stdio: Use the standard. Don't assume that
+ * MS or MinGW will support the "I" qualifier indefinitely. */
+#    define SIZE_T_FMT   "z"
+#    define T_UINT64_FMT "j"
+#    define T_INT64_FMT  "j"
+#  elif (_MSC_VER < 1900 && defined(_WIN64)) || defined(__MINGW64__)
+/* VS 2013 and earlier, 64-bit: use Microsoft's "I" qualifier. */
+#    define SIZE_T_FMT   "I64"
+#    define T_UINT64_FMT "I64"
+#    define T_INT64_FMT  "I64"
+#  elif (_MSC_VER < 1900 && defined(_WIN32)) || defined(__MINGW32__)
+/* VS 2013 and earlier, 32-bit: use Microsoft's "I" qualifier. */
+#    define SIZE_T_FMT   "I32"
+#    define T_UINT64_FMT "I64"
+#    define T_INT64_FMT  "I64"
 #  endif
 
-#  define T_UINT64_FMT   "I64"
-#  define T_INT64_FMT    "I64"
+#  define LL_FMT         "ll"
 #  define POINTER_FMT    "p"
 
 #elif defined(__GNU_LIBRARY__) || defined(__GLIBC__) || defined(__GLIBC_MINOR__) || \