diff --git a/Makefile b/Makefile
index a01962f..11ab14b 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@ BINDING=target/vulkan.rs
 NATIVE_DIR=target/native
 TARGET=$(NATIVE_DIR)/test
 OBJECTS=$(NATIVE_DIR)/test.o $(NATIVE_DIR)/window.o
-LIBRARY=target/debug/libportability.a
+LIBRARY=target/debug/libportability.so
 
 CC=g++
 CFLAGS=-std=c++11 -ggdb -O0 -I$(VULKAN_DIR)
@@ -20,7 +20,7 @@ $(BINDING): $(VULKAN_DIR)/vulkan/*.h
 	bindgen --no-layout-tests --rustfmt-bindings $(VULKAN_DIR)/vulkan/vulkan.h -o $(BINDING)
 
 $(LIBRARY): libportability/src/*.rs libportability-gfx/src/*.rs Cargo.toml $(wildcard Cargo.lock)
-	cargo build -p portability
+	cargo build --manifest-path libportability/Cargo.toml --features vulkan
 	mkdir -p target/native
 
 $(NATIVE_DIR)/%.o: native/%.cpp $(DEPS) Makefile
diff --git a/README.md b/README.md
index 153f37b..fbdad59 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ make
 Build the Rust library (portability implementation):
 
 ```
-cargo build -p portability
+cargo build --manifest-path libportability/Cargo.toml --features <vulkan|dx12>
 ```
 
 Build the native example:
diff --git a/native/math.hpp b/native/math.hpp
index 5165ceb..88ed5ea 100644
--- a/native/math.hpp
+++ b/native/math.hpp
@@ -1,7 +1,9 @@
 
 #pragma once
 
-const float M_PI = 3.1415926535897932;
+#include <cmath>
+
+const float pi = 3.1415926535897932;
 
 template<typename T>
 class mat4_tl
@@ -85,7 +87,7 @@ template<typename T>
 auto perspective(T fov, T aspect, T n, T f) -> mat4_tl<T> {
     assert(fov > 0); assert(aspect > 0);
 
-    const T rad = fov*T(M_PI)/T(180);
+    const T rad = fov*T(pi)/T(180);
     const T a = T(1)/(std::tan(rad/T(2)));
 
     return mat4_tl<T>(
@@ -101,7 +103,7 @@ class vec3_tl
 public:
     union {
         struct { T x, y, z; };
-        struct { T s, t, r; };
+        struct { T s, t, u; };
         struct { T r, g, b; };
         T data[3];
     };