diff --git a/src/win32/posix_w32.c b/src/win32/posix_w32.c
index 7b82d0961..14f30ebe5 100644
--- a/src/win32/posix_w32.c
+++ b/src/win32/posix_w32.c
@@ -44,6 +44,119 @@
 /* GetFinalPathNameByHandleW signature */
 typedef DWORD(WINAPI *PFGetFinalPathNameByHandleW)(HANDLE, LPWSTR, DWORD, DWORD);
 
+GIT_INLINE(void) set_errno(void)
+{
+	switch (GetLastError()) {
+	case ERROR_FILE_NOT_FOUND:
+	case ERROR_PATH_NOT_FOUND:
+	case ERROR_INVALID_DRIVE:
+	case ERROR_NO_MORE_FILES:
+	case ERROR_BAD_NETPATH:
+	case ERROR_BAD_NET_NAME:
+	case ERROR_BAD_PATHNAME:
+	case ERROR_FILENAME_EXCED_RANGE:
+		errno = ENOENT;
+		break;
+	case ERROR_BAD_ENVIRONMENT:
+		errno = E2BIG;
+		break;
+	case ERROR_BAD_FORMAT:
+	case ERROR_INVALID_STARTING_CODESEG:
+	case ERROR_INVALID_STACKSEG:
+	case ERROR_INVALID_MODULETYPE:
+	case ERROR_INVALID_EXE_SIGNATURE:
+	case ERROR_EXE_MARKED_INVALID:
+	case ERROR_BAD_EXE_FORMAT:
+	case ERROR_ITERATED_DATA_EXCEEDS_64k:
+	case ERROR_INVALID_MINALLOCSIZE:
+	case ERROR_DYNLINK_FROM_INVALID_RING:
+	case ERROR_IOPL_NOT_ENABLED:
+	case ERROR_INVALID_SEGDPL:
+	case ERROR_AUTODATASEG_EXCEEDS_64k:
+	case ERROR_RING2SEG_MUST_BE_MOVABLE:
+	case ERROR_RELOC_CHAIN_XEEDS_SEGLIM:
+	case ERROR_INFLOOP_IN_RELOC_CHAIN:
+		errno = ENOEXEC;
+		break;
+	case ERROR_INVALID_HANDLE:
+	case ERROR_INVALID_TARGET_HANDLE:
+	case ERROR_DIRECT_ACCESS_HANDLE:
+		errno = EBADF;
+		break;
+	case ERROR_WAIT_NO_CHILDREN:
+	case ERROR_CHILD_NOT_COMPLETE:
+		errno = ECHILD;
+		break;
+	case ERROR_NO_PROC_SLOTS:
+	case ERROR_MAX_THRDS_REACHED:
+	case ERROR_NESTING_NOT_ALLOWED:
+		errno = EAGAIN;
+		break;
+	case ERROR_ARENA_TRASHED:
+	case ERROR_NOT_ENOUGH_MEMORY:
+	case ERROR_INVALID_BLOCK:
+	case ERROR_NOT_ENOUGH_QUOTA:
+		errno = ENOMEM;
+		break;
+	case ERROR_ACCESS_DENIED:
+	case ERROR_CURRENT_DIRECTORY:
+	case ERROR_WRITE_PROTECT:
+	case ERROR_BAD_UNIT:
+	case ERROR_NOT_READY:
+	case ERROR_BAD_COMMAND:
+	case ERROR_CRC:
+	case ERROR_BAD_LENGTH:
+	case ERROR_SEEK:
+	case ERROR_NOT_DOS_DISK:
+	case ERROR_SECTOR_NOT_FOUND:
+	case ERROR_OUT_OF_PAPER:
+	case ERROR_WRITE_FAULT:
+	case ERROR_READ_FAULT:
+	case ERROR_GEN_FAILURE:
+	case ERROR_SHARING_VIOLATION:
+	case ERROR_LOCK_VIOLATION:
+	case ERROR_WRONG_DISK:
+	case ERROR_SHARING_BUFFER_EXCEEDED:
+	case ERROR_NETWORK_ACCESS_DENIED:
+	case ERROR_CANNOT_MAKE:
+	case ERROR_FAIL_I24:
+	case ERROR_DRIVE_LOCKED:
+	case ERROR_SEEK_ON_DEVICE:
+	case ERROR_NOT_LOCKED:
+	case ERROR_LOCK_FAILED:
+		errno = EACCES;
+		break;
+	case ERROR_FILE_EXISTS:
+	case ERROR_ALREADY_EXISTS:
+		errno = EEXIST;
+		break;
+	case ERROR_NOT_SAME_DEVICE:
+		errno = EXDEV;
+		break;
+	case ERROR_INVALID_FUNCTION:
+	case ERROR_INVALID_ACCESS:
+	case ERROR_INVALID_DATA:
+	case ERROR_INVALID_PARAMETER:
+	case ERROR_NEGATIVE_SEEK:
+		errno = EINVAL;
+		break;
+	case ERROR_TOO_MANY_OPEN_FILES:
+		errno = EMFILE;
+		break;
+	case ERROR_DISK_FULL:
+		errno = ENOSPC;
+		break;
+	case ERROR_BROKEN_PIPE:
+		errno = EPIPE;
+		break;
+	case ERROR_DIR_NOT_EMPTY:
+		errno = ENOTEMPTY;
+		break;
+	default:
+		errno = EINVAL;
+	}
+}
+
 /**
  * Truncate or extend file.
  *