diff --git a/README.md b/README.md
index 7f91d8d7..753a1e10 100644
--- a/README.md
+++ b/README.md
@@ -115,6 +115,7 @@ The length sub-specifier modifies the length of the data type.
 | (none) | int  | unsigned int |
 | l      | long int | unsigned long int |
 | ll     | long long int | unsigned long long int |
+| z      | size_t int | unsigned size_t int |
 
 
 ## Compiler switches/defines
diff --git a/printf.c b/printf.c
index a65f4185..e5e3a369 100644
--- a/printf.c
+++ b/printf.c
@@ -425,6 +425,10 @@ static size_t _vsnprintf(char* buffer, size_t buffer_len, const char* format, va
       flags |= FLAGS_LONG_LONG;
       format++;
     }
+    if (*format == 'z') {
+      flags |= (sizeof(size_t) == sizeof(long) ? FLAGS_LONG : FLAGS_LONG_LONG);
+      format++;
+    }
 
     // evaluate specifier
     switch (*format) {
diff --git a/test/test_suite.cpp b/test/test_suite.cpp
index e241195e..0a51e09b 100644
--- a/test/test_suite.cpp
+++ b/test/test_suite.cpp
@@ -1,6 +1,6 @@
 ///////////////////////////////////////////////////////////////////////////////
 // \author (c) Marco Paland (info@paland.com)
-//             2017, PALANDesign Hannover, Germany
+//             2017-2018, PALANDesign Hannover, Germany
 //
 // \license The MIT License (MIT)
 //
@@ -923,6 +923,21 @@ TEST_CASE("types", "[]" ) {
   test::sprintf(buffer, "%llu", 18446744073709551615LLU);
   REQUIRE(!strcmp(buffer, "18446744073709551615"));
 
+  test::sprintf(buffer, "%zu", 2147483647UL);
+  REQUIRE(!strcmp(buffer, "2147483647"));
+
+  test::sprintf(buffer, "%zd", 2147483647UL);
+  REQUIRE(!strcmp(buffer, "2147483647"));
+
+  if (sizeof(size_t) == sizeof(long)) {
+    test::sprintf(buffer, "%zi", -2147483647L);
+    REQUIRE(!strcmp(buffer, "-2147483647"));
+  }
+  else {
+    test::sprintf(buffer, "%zi", -2147483647LL);
+    REQUIRE(!strcmp(buffer, "-2147483647"));
+  }
+
   test::sprintf(buffer, "%b", 60000);
   REQUIRE(!strcmp(buffer, "1110101001100000"));