diff --git a/src/core/ffi.c b/src/core/ffi.c
index f48d1ba5..0e5de3de 100644
--- a/src/core/ffi.c
+++ b/src/core/ffi.c
@@ -1178,7 +1178,13 @@ static Janet janet_ffi_win64(JanetFFISignature *signature, void *function_pointe
 
     /* hack to get proper stack placement and avoid clobbering from logic above - shift stack down, otherwise we have issues.
      * Technically, this writes into 16 bytes of unallocated stack memory */
+#ifdef JANET_MINGW
+#pragma GCC diagnostic ignored "-Wstringop-overflow"
+#endif
     if (stack_size) memmove(stack - stack_shift, stack, stack_size);
+#ifdef JANET_MINGW
+#pragma GCC diagnostic pop
+#endif
 
     switch (signature->variant) {
         default:
diff --git a/src/core/os.c b/src/core/os.c
index 4d5c8772..9ed397c0 100644
--- a/src/core/os.c
+++ b/src/core/os.c
@@ -118,6 +118,7 @@ JANET_CORE_FN(os_which,
               "(os/which)",
               "Check the current operating system. Returns one of:\n\n"
               "* :windows\n\n"
+              "* :mingw\n\n"
               "* :macos\n\n"
               "* :web - Web assembly (emscripten)\n\n"
               "* :linux\n\n"
@@ -130,6 +131,8 @@ JANET_CORE_FN(os_which,
     (void) argv;
 #if defined(JANET_OS_NAME)
     return janet_ckeywordv(janet_stringify(JANET_OS_NAME));
+#elif defined(JANET_MINGW)
+    return janet_ckeywordv("mingw");
 #elif defined(JANET_WINDOWS)
     return janet_ckeywordv("windows");
 #elif defined(JANET_APPLE)
@@ -445,7 +448,9 @@ typedef struct {
 static JanetEVGenericMessage janet_proc_wait_subr(JanetEVGenericMessage args) {
     JanetProc *proc = (JanetProc *) args.argp;
     WaitForSingleObject(proc->pHandle, INFINITE);
-    GetExitCodeProcess(proc->pHandle, (LPDWORD) &args.tag);
+    DWORD exitcode = 0;
+    GetExitCodeProcess(proc->pHandle, &exitcode);
+    args.tag = (int32_t) exitcode;
     return args;
 }
 
diff --git a/src/include/janet.h b/src/include/janet.h
index 0eaa2178..8815fe31 100644
--- a/src/include/janet.h
+++ b/src/include/janet.h
@@ -97,6 +97,11 @@ extern "C" {
 #define JANET_MSVC
 #endif
 
+/* Check Mingw 32-bit and 64-bit */
+#ifdef __MINGW32__
+#define JANET_MINGW
+#endif
+
 /* Check 64-bit vs 32-bit */
 #if ((defined(__x86_64__) || defined(_M_X64)) \
      && (defined(JANET_POSIX) || defined(JANET_WINDOWS))) \
diff --git a/test/suite0010.janet b/test/suite0010.janet
index 98e0ad4d..e3db6818 100644
--- a/test/suite0010.janet
+++ b/test/suite0010.janet
@@ -144,7 +144,7 @@
 (assert (< 1000 1e23) "greater than immediate 2")
 
 # os/execute with environment variables
-(assert (= 0 (os/execute [(dyn :executable) "-e" "(+ 1 2 3)"] :pe {"HELLO" "WORLD"})) "os/execute with env")
+(assert (= 0 (os/execute [(dyn :executable) "-e" "(+ 1 2 3)"] :pe (merge (os/environ) {"HELLO" "WORLD"}))) "os/execute with env")
 
 # Regression #638
 (compwhen