diff --git a/format.cc b/format.cc
index df031371..a612f0c3 100644
--- a/format.cc
+++ b/format.cc
@@ -42,6 +42,9 @@
 
 #ifdef _WIN32
 # define WIN32_LEAN_AND_MEAN
+# ifdef __MINGW32__
+#  include <cstring>
+# endif
 # include <windows.h>
 # undef ERROR
 #endif
@@ -228,7 +231,11 @@ int fmt::internal::StrError(
     result = ERANGE;
   buffer = message;
 #elif _WIN32
+# ifdef __MINGW32__
+  strerror(result);
+# else
   result = strerror_s(buffer, buffer_size, error_code);
+# endif
   // If the buffer is full then the message is probably truncated.
   if (result == 0 && std::strlen(buffer) == buffer_size - 1)
     result = ERANGE;
diff --git a/format.h b/format.h
index 6d37ec96..b1c45bb6 100644
--- a/format.h
+++ b/format.h
@@ -61,9 +61,13 @@
 // Compatibility with compilers other than clang.
 #ifdef __has_feature
 # define FMT_HAS_FEATURE(x) __has_feature(x)
-# define FMT_HAS_BUILTIN(x) __has_builtin(x)
 #else
 # define FMT_HAS_FEATURE(x) 0
+#endif
+
+#ifdef __has_builtin
+# define FMT_HAS_BUILTIN(x) __has_builtin(x)
+#else
 # define FMT_HAS_BUILTIN(x) 0
 #endif
 
@@ -311,7 +315,7 @@ template <typename T, std::size_t SIZE>
 void Array<T, SIZE>::append(const T *begin, const T *end) {
   std::ptrdiff_t num_elements = end - begin;
   if (size_ + num_elements > capacity_)
-    Grow(num_elements);
+    Grow(size_ + num_elements);
   std::copy(begin, end, CheckPtr(ptr_, capacity_) + size_);
   size_ += num_elements;
 }
diff --git a/posix.cc b/posix.cc
index 9c3cc2ca..2d3a85d3 100644
--- a/posix.cc
+++ b/posix.cc
@@ -41,6 +41,10 @@
 # define S_IRUSR _S_IREAD
 # define S_IWUSR _S_IWRITE
 
+# ifdef __MINGW32__
+#  define _SH_DENYNO 0x40
+# endif
+
 #endif  // _WIN32
 
 namespace {
diff --git a/test/format-test.cc b/test/format-test.cc
index 95ca2dc2..28b62112 100644
--- a/test/format-test.cc
+++ b/test/format-test.cc
@@ -35,7 +35,7 @@
 #include <memory>
 #include <sstream>
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__MINGW32__)
 // Fix MSVC warning about "unsafe" fopen.
 FILE *FOpen(const char *filename, const char *mode) {
   FILE *f = 0;
diff --git a/test/gtest-extra-test.cc b/test/gtest-extra-test.cc
index 5d5c678b..af2682f4 100644
--- a/test/gtest-extra-test.cc
+++ b/test/gtest-extra-test.cc
@@ -32,13 +32,13 @@
 #include <stdexcept>
 #include <gtest/gtest-spi.h>
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__MINGW32__)
 # include <crtdbg.h>  // for _CrtSetReportMode
 #endif  // _WIN32
 
 namespace {
 
-#ifdef _WIN32
+#if defined(_WIN32) && !defined(__MINGW32__)
 
 // Suppresses Windows assertions on invalid file descriptors, making
 // POSIX functions return proper error codes instead of crashing on Windows.
diff --git a/test/util-test.cc b/test/util-test.cc
index 35a5e410..66ee4727 100644
--- a/test/util-test.cc
+++ b/test/util-test.cc
@@ -43,7 +43,7 @@ using fmt::StringRef;
 
 namespace {
 std::string GetSystemErrorMessage(int error_code) {
-#ifndef _WIN32
+#if defined(__MINGW32__) || !defined(_WIN32)
   return strerror(error_code);
 #else
   enum { BUFFER_SIZE = 200 };