diff --git a/README.md b/README.md
index 49a6755f..40083525 100644
--- a/README.md
+++ b/README.md
@@ -42,7 +42,7 @@ that's it.
 If the build system is unable to find your GMP installation, please edit the paths in file makeConstants.  In general, the project uses a basic makefile.  In the event that you have to do something more complicated to get the library to compile, or if you are unable to get it to compile, please e-mail me or open an issue on GitHub.  Doing so is much more effective than cursing at your computer, and will save other users trouble in the future.
 
 
-Windows
+Windows Native
 ----
 
 Cork uses C++11, so you will need the most recent compiler; Visual Studio 2012 or higher please.  You will also need to install the MPIR arithmetic library into your Visual Studio environment.
@@ -50,6 +50,15 @@ Cork uses C++11, so you will need the most recent compiler; Visual Studio 2012 o
 Once this is done, you can use the solution and project files in the /win/ subdirectory to build the demo program.  The solution/project is not currently configured to build a DLL.  Please bug me if this is an issue for you.
 
 
+Cross-Compiling on Unix for Windows
+-----------------------------------
+
+Cork can be cross compiled for windows using [mingw-w64](http://mingw-w64.sourceforge.net) and [wclang](https://github.com/tpoechtrager/wclang) which is a clang frontend for mingw. You first need to cross compile the GMP library using mingw-w64 and then:
+
+    make CC=w32-clang CXX=w32-clang++ GMP_INC_DIR=/usr/i686-w64-mingw32/include/ GMP_LIB_DIR=/usr/i686-w64-mingw32/lib/
+
+Tune the `GMP_INC_DIR` and `GMP_LIB_DIR` variables according to where gmp was compiled. It should build a Windows executable under `bin/cork`. You can rename it `cork.exe` and you are set.
+
 Licensing
 =========
 
diff --git a/src/isct/fixint.h b/src/isct/fixint.h
index 37465a1d..ccc20740 100644
--- a/src/isct/fixint.h
+++ b/src/isct/fixint.h
@@ -45,7 +45,7 @@
 
 
 
-#ifdef _WIN32
+#ifdef _MSC_VER
 #include <mpir.h>
 #else
 #include <gmp.h>
diff --git a/src/isct/gmpext4.h b/src/isct/gmpext4.h
index 1a5541c9..fb76fab6 100644
--- a/src/isct/gmpext4.h
+++ b/src/isct/gmpext4.h
@@ -25,7 +25,7 @@
 // +-------------------------------------------------------------------------
 #pragma once
 
-#ifdef _WIN32
+#ifdef _MSC_VER
 #pragma warning(disable: 4800)
 #pragma warning(disable: 4244)
 #include <mpirxx.h>
diff --git a/src/mesh/mesh.isct.tpp b/src/mesh/mesh.isct.tpp
index 6c48930a..9c2b16d2 100644
--- a/src/mesh/mesh.isct.tpp
+++ b/src/mesh/mesh.isct.tpp
@@ -632,7 +632,7 @@ public:
         quantized_coords.resize(N);
         uint write = 0;
         TopoCache::verts.for_each([&](Vptr v) {
-#ifdef _WIN32
+#ifdef _MSC_VER
             Vec3d raw = mesh->verts[v->ref].pos;
 #else
             Vec3d raw = TopoCache::mesh->verts[v->ref].pos;
diff --git a/src/mesh/mesh.tpp b/src/mesh/mesh.tpp
index 9da1614d..bc63204d 100644
--- a/src/mesh/mesh.tpp
+++ b/src/mesh/mesh.tpp
@@ -250,7 +250,7 @@ typename Mesh<VertData,TriData>::NeighborCache
 }
 
 // This function signature is an amazing disaster...
-#ifdef _WIN32
+#ifdef _MSC_VER
 template<class VertData, class TriData>
 template<class Edata>
 typename Mesh<VertData,TriData>::EGraphCache<Edata>
diff --git a/src/util/prelude.h b/src/util/prelude.h
index 00329aad..24a03b16 100644
--- a/src/util/prelude.h
+++ b/src/util/prelude.h
@@ -31,6 +31,10 @@
 #include <algorithm>
 #include <iostream>
 
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
 #ifndef uint
 typedef unsigned int uint;
 #endif