diff --git a/tests/stdio_test.cpp b/tests/stdio_test.cpp
index c20597b..9cb0ffd 100644
--- a/tests/stdio_test.cpp
+++ b/tests/stdio_test.cpp
@@ -3487,28 +3487,51 @@
 #endif
 }
 
-TEST(STDIO_TEST, sscanf_w_base) {
+TEST(STDIO_TEST, sscanf_w_or_wf_base) {
 #if defined(__BIONIC__)
 #pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wformat"
 #pragma clang diagnostic ignored "-Wformat-invalid-specifier"
   int8_t a;
   EXPECT_EQ(1, sscanf("<0b101>", "<%w8b>", &a));
   EXPECT_EQ(0b101, a);
+  int_fast8_t fast_a;
+  EXPECT_EQ(1, sscanf("<0b101>", "<%wf8b>", &fast_a));
+  EXPECT_EQ(0b101, fast_a);
   int8_t b1;
   EXPECT_EQ(1, sscanf("<0xFF>", "<%w8i>", &b1));
   EXPECT_EQ(-1, b1);
   int8_t b2;
   EXPECT_EQ(1, sscanf("<0x1FF>", "<%w8i>", &b2));
   EXPECT_EQ(-1, b2);
+  int_fast8_t fast_b;
+  EXPECT_EQ(1, sscanf("<0x1234123412341234>", "<%wf8x>", &fast_b));
+  EXPECT_EQ(0x34, fast_b);
   int16_t c1;
   EXPECT_EQ(1, sscanf("<0xFFFF>", "<%w16i>", &c1));
   EXPECT_EQ(-1, c1);
   uint16_t c2;
   EXPECT_EQ(1, sscanf("<64>", "<%w16d>", &c2));
   EXPECT_EQ(64, c2);
+  int_fast16_t fast_c;
+#if defined(__LP64__)
+  EXPECT_EQ(1, sscanf("<0x1111111122222222>", "<%wf16x>", &fast_c));
+  EXPECT_EQ(0x1111111122222222, fast_c);
+#else
+  EXPECT_EQ(1, sscanf("<0x1111111122222222>", "<%wf16x>", &fast_c));
+  EXPECT_EQ(0x22222222, fast_c);
+#endif
   int32_t d;
   EXPECT_EQ(1, sscanf("<021>", "<%w32o>", &d));
   EXPECT_EQ(021, d);
+  int_fast32_t fast_d;
+#if defined(__LP64__)
+  EXPECT_EQ(1, sscanf("<0x3333333344444444>", "<%wf32x>", &fast_d));
+  EXPECT_EQ(0x3333333344444444, fast_d);
+#else
+  EXPECT_EQ(1, sscanf("<0x3333333344444444>", "<%wf32x>", &fast_d));
+  EXPECT_EQ(0x44444444, fast_d);
+#endif
   uint32_t e;
   EXPECT_EQ(1, sscanf("<-1>", "<%w32u>", &e));
   EXPECT_EQ(4294967295, e);
@@ -3517,6 +3540,11 @@
   EXPECT_EQ(0x3b, f);
   EXPECT_EQ(1, sscanf("<0x3b>", "<%w64X>", &f));
   EXPECT_EQ(0x3B, f);
+  uint_fast64_t fast_f;
+  EXPECT_EQ(1, sscanf("<0xaaaaaaaa>", "<%wf64x>", &fast_f));
+  EXPECT_EQ(0xaaaaaaaa, fast_f);
+  EXPECT_EQ(1, sscanf("<0xaaaaaaaa>", "<%wf64X>", &fast_f));
+  EXPECT_EQ(0xAAAAAAAA, fast_f);
 #pragma clang diagnostic pop
 #else
   GTEST_SKIP() << "no %w in glibc";
@@ -3544,40 +3572,66 @@
 #endif
 }
 
-TEST(STDIO_TEST, sscanf_invalid_w_width) {
+TEST(STDIO_TEST, sscanf_invalid_w_or_wf_width) {
 #if defined(__BIONIC__)
 #pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wformat"
 #pragma clang diagnostic ignored "-Wformat-invalid-specifier"
   int32_t a;
   EXPECT_DEATH(sscanf("<100>", "<%w20d>", &a), "%w20 is unsupported");
+  int_fast32_t fast_a;
+  EXPECT_DEATH(sscanf("<100>", "<%wf20d>", &fast_a), "%wf20 is unsupported");
 #pragma clang diagnostic pop
 #else
   GTEST_SKIP() << "no %w in glibc";
 #endif
 }
 
-TEST(STDIO_TEST, swscanf_w_base) {
+TEST(STDIO_TEST, swscanf_w_or_wf_base) {
 #if defined(__BIONIC__)
 #pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wformat"
 #pragma clang diagnostic ignored "-Wformat-invalid-specifier"
   int8_t a;
   EXPECT_EQ(1, swscanf(L"<0b101>", L"<%w8b>", &a));
   EXPECT_EQ(0b101, a);
+  int_fast8_t fast_a;
+  EXPECT_EQ(1, swscanf(L"<0b101>", L"<%wf8b>", &fast_a));
+  EXPECT_EQ(0b101, fast_a);
   int8_t b1;
   EXPECT_EQ(1, swscanf(L"<0xFF>", L"<%w8i>", &b1));
   EXPECT_EQ(-1, b1);
   int8_t b2;
   EXPECT_EQ(1, swscanf(L"<0x1FF>", L"<%w8i>", &b2));
   EXPECT_EQ(-1, b2);
+  int_fast8_t fast_b;
+  EXPECT_EQ(1, swscanf(L"<0x1234123412341234>", L"<%wf8i>", &fast_b));
+  EXPECT_EQ(0x34, fast_b);
   int16_t c1;
   EXPECT_EQ(1, swscanf(L"<0xFFFF>", L"<%w16i>", &c1));
   EXPECT_EQ(-1, c1);
   uint16_t c2;
   EXPECT_EQ(1, swscanf(L"<64>", L"<%w16d>", &c2));
   EXPECT_EQ(64, c2);
+  int_fast16_t fast_c;
+#if defined(__LP64__)
+  EXPECT_EQ(1, swscanf(L"<0x1111111122222222>", L"<%wf16x>", &fast_c));
+  EXPECT_EQ(0x1111111122222222, fast_c);
+#else
+  EXPECT_EQ(1, swscanf(L"<0x1111111122222222>", L"<%wf16x>", &fast_c));
+  EXPECT_EQ(0x22222222, fast_c);
+#endif
   int32_t d;
   EXPECT_EQ(1, swscanf(L"<021>", L"<%w32o>", &d));
   EXPECT_EQ(021, d);
+  int_fast32_t fast_d;
+#if defined(__LP64__)
+  EXPECT_EQ(1, swscanf(L"<0x3333333344444444>", L"<%wf32x>", &fast_d));
+  EXPECT_EQ(0x3333333344444444, fast_d);
+#else
+  EXPECT_EQ(1, swscanf(L"<0x3333333344444444>", L"<%wf32x>", &fast_d));
+  EXPECT_EQ(0x44444444, fast_d);
+#endif
   uint32_t e;
   EXPECT_EQ(1, swscanf(L"<-1>", L"<%w32u>", &e));
   EXPECT_EQ(4294967295, e);
@@ -3586,6 +3640,11 @@
   EXPECT_EQ(0x3b, f);
   EXPECT_EQ(1, swscanf(L"<0x3b>", L"<%w64X>", &f));
   EXPECT_EQ(0x3B, f);
+  uint_fast64_t fast_f;
+  EXPECT_EQ(1, swscanf(L"<0xaaaaaaaa>", L"<%wf64x>", &fast_f));
+  EXPECT_EQ(0xaaaaaaaa, fast_f);
+  EXPECT_EQ(1, swscanf(L"<0xaaaaaaaa>", L"<%wf64X>", &fast_f));
+  EXPECT_EQ(0xAAAAAAAA, fast_f);
 #pragma clang diagnostic pop
 #else
   GTEST_SKIP() << "no %w in glibc";
@@ -3613,12 +3672,15 @@
 #endif
 }
 
-TEST(STDIO_TEST, swscanf_invalid_w_width) {
+TEST(STDIO_TEST, swscanf_invalid_w_or_wf_width) {
 #if defined(__BIONIC__)
 #pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wformat"
 #pragma clang diagnostic ignored "-Wformat-invalid-specifier"
   int32_t a;
   EXPECT_DEATH(swscanf(L"<100>", L"<%w20d>", &a), "%w20 is unsupported");
+  int_fast32_t fast_a;
+  EXPECT_DEATH(swscanf(L"<100>", L"<%wf20d>", &fast_a), "%wf20 is unsupported");
 #pragma clang diagnostic pop
 #else
   GTEST_SKIP() << "no %w in glibc";