diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0ae75e156..bcf8160c1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,10 @@ v0.25 + 1
 
 ### API additions
 
+* You can now set the default share mode on Windows for opening files using
+  `GIT_OPT_SET_WINDOWS_SHAREMODE` option with `git_libgit2_opts()`.
+  You can query the current share mode with `GIT_OPT_GET_WINDOWS_SHAREMODE`.
+
 ### API removals
 
 ### Breaking API changes
diff --git a/include/git2/common.h b/include/git2/common.h
index c909f86ca..6d2092028 100644
--- a/include/git2/common.h
+++ b/include/git2/common.h
@@ -180,6 +180,8 @@ typedef enum {
 	GIT_OPT_GET_USER_AGENT,
 	GIT_OPT_ENABLE_OFS_DELTA,
 	GIT_OPT_ENABLE_SYNCHRONOUS_OBJECT_CREATION,
+	GIT_OPT_GET_WINDOWS_SHAREMODE,
+	GIT_OPT_SET_WINDOWS_SHAREMODE,
 } git_libgit2_opt_t;
 
 /**
@@ -284,6 +286,17 @@ typedef enum {
  *		> - `user_agent` is the value that will be delivered as the
  *		>   User-Agent header on HTTP requests.
  *
+ *	* opts(GIT_OPT_SET_WINDOWS_SHAREMODE, unsigned long value)
+ *
+ *		> Set the share mode used when opening files on Windows.
+ *		> For more information, see the documentation for CreateFile.
+ *		> The default is: FILE_SHARE_READ | FILE_SHARE_WRITE.  This is
+ *		> ignored and unused on non-Windows platforms.
+ *
+ *	* opts(GIT_OPT_GET_WINDOWS_SHAREMODE, unsigned long *value)
+ *
+ *		> Get the share mode used when opening files on Windows.
+ *
  *	* opts(GIT_OPT_ENABLE_STRICT_OBJECT_CREATION, int enabled)
  *
  *		> Enable strict input validation when creating new objects
diff --git a/src/settings.c b/src/settings.c
index 24e549ec1..07ac16a8f 100644
--- a/src/settings.c
+++ b/src/settings.c
@@ -231,6 +231,18 @@ int git_libgit2_opts(int key, ...)
 		git_object__synchronous_writing = (va_arg(ap, int) != 0);
 		break;
 
+	case GIT_OPT_GET_WINDOWS_SHAREMODE:
+#ifdef GIT_WIN32
+		*(va_arg(ap, unsigned long *)) = git_win32__createfile_sharemode;
+#endif
+		break;
+
+	case GIT_OPT_SET_WINDOWS_SHAREMODE:
+#ifdef GIT_WIN32
+		git_win32__createfile_sharemode = va_arg(ap, unsigned long);
+#endif
+		break;
+
 	default:
 		giterr_set(GITERR_INVALID, "invalid option key");
 		error = -1;
diff --git a/src/win32/posix.h b/src/win32/posix.h
index 73705fb2b..0ba05a16f 100644
--- a/src/win32/posix.h
+++ b/src/win32/posix.h
@@ -14,6 +14,8 @@
 #include "utf-conv.h"
 #include "dir.h"
 
+extern unsigned long git_win32__createfile_sharemode;
+
 typedef SOCKET GIT_SOCKET;
 
 #define p_lseek(f,n,w) _lseeki64(f, n, w)
diff --git a/src/win32/posix_w32.c b/src/win32/posix_w32.c
index 28cd3e2e9..4943ce202 100644
--- a/src/win32/posix_w32.c
+++ b/src/win32/posix_w32.c
@@ -26,15 +26,6 @@
 #define IO_REPARSE_TAG_SYMLINK (0xA000000CL)
 #endif
 
-/* Options which we always provide to _wopen.
- *
- * _O_BINARY - Raw access; no translation of CR or LF characters
- * _O_NOINHERIT - Do not mark the created handle as inheritable by child processes.
- *    The Windows default is 'not inheritable', but the CRT's default (following
- *    POSIX convention) is 'inheritable'. We have no desire for our handles to be
- *    inheritable on Windows, so specify the flag to get default behavior back. */
-#define STANDARD_OPEN_FLAGS (_O_BINARY | _O_NOINHERIT)
-
 /* Allowable mode bits on Win32.  Using mode bits that are not supported on
  * Win32 (eg S_IRWXU) is generally ignored, but Wine warns loudly about it
  * so we simply remove them.
@@ -44,6 +35,9 @@
 /* GetFinalPathNameByHandleW signature */
 typedef DWORD(WINAPI *PFGetFinalPathNameByHandleW)(HANDLE, LPWSTR, DWORD, DWORD);
 
+unsigned long git_win32__createfile_sharemode =
+ FILE_SHARE_READ | FILE_SHARE_WRITE;
+
 GIT_INLINE(void) set_errno(void)
 {
 	switch (GetLastError()) {
@@ -489,7 +483,7 @@ int p_open(const char *path, int flags, ...)
 		break;
 	}
 
-	sharing = FILE_SHARE_READ | FILE_SHARE_WRITE;
+	sharing = (DWORD)git_win32__createfile_sharemode;
 
 	switch (flags & (O_CREAT | O_TRUNC | O_EXCL)) {
 	case O_CREAT | O_EXCL:
@@ -510,7 +504,8 @@ int p_open(const char *path, int flags, ...)
 		break;
 	}
 
-	attributes = (mode & S_IWRITE) ? FILE_ATTRIBUTE_NORMAL : FILE_ATTRIBUTE_READONLY;
+	attributes = ((flags & O_CREAT) && !(mode & S_IWRITE)) ?
+		FILE_ATTRIBUTE_READONLY : FILE_ATTRIBUTE_NORMAL;
 	osf_flags = flags & (O_RDONLY | O_APPEND);
 
 	do_with_retries(