diff --git a/src/pkg/runtime/windows/386/defs.h b/src/pkg/runtime/windows/386/defs.h
index 6cc5336a94e..e64a82fafee 100644
--- a/src/pkg/runtime/windows/386/defs.h
+++ b/src/pkg/runtime/windows/386/defs.h
@@ -31,6 +31,20 @@ enum {
 // Types
 #pragma pack on
 
+typedef struct SystemInfo SystemInfo;
+struct SystemInfo {
+	byte Pad_godefs_0[4];
+	uint32 dwPageSize;
+	void *lpMinimumApplicationAddress;
+	void *lpMaximumApplicationAddress;
+	uint32 dwActiveProcessorMask;
+	uint32 dwNumberOfProcessors;
+	uint32 dwProcessorType;
+	uint32 dwAllocationGranularity;
+	uint16 wProcessorLevel;
+	uint16 wProcessorRevision;
+};
+
 typedef struct ExceptionRecord ExceptionRecord;
 struct ExceptionRecord {
 	uint32 ExceptionCode;
diff --git a/src/pkg/runtime/windows/amd64/defs.h b/src/pkg/runtime/windows/amd64/defs.h
index d5191a3d743..da4c19d90b7 100644
--- a/src/pkg/runtime/windows/amd64/defs.h
+++ b/src/pkg/runtime/windows/amd64/defs.h
@@ -31,6 +31,20 @@ enum {
 // Types
 #pragma pack on
 
+typedef struct SystemInfo SystemInfo;
+struct SystemInfo {
+	byte Pad_godefs_0[4];
+	uint32 dwPageSize;
+	void *lpMinimumApplicationAddress;
+	void *lpMaximumApplicationAddress;
+	uint64 dwActiveProcessorMask;
+	uint32 dwNumberOfProcessors;
+	uint32 dwProcessorType;
+	uint32 dwAllocationGranularity;
+	uint16 wProcessorLevel;
+	uint16 wProcessorRevision;
+};
+
 typedef struct ExceptionRecord ExceptionRecord;
 struct ExceptionRecord {
 	uint32 ExceptionCode;
diff --git a/src/pkg/runtime/windows/defs.c b/src/pkg/runtime/windows/defs.c
index 1b07dfbc192..7cfd9ad0f71 100644
--- a/src/pkg/runtime/windows/defs.c
+++ b/src/pkg/runtime/windows/defs.c
@@ -38,6 +38,7 @@ enum {
 	$EXCEPTION_INT_OVERFLOW = STATUS_INTEGER_OVERFLOW,
 };
 
+typedef SYSTEM_INFO $SystemInfo;
 typedef EXCEPTION_RECORD $ExceptionRecord;
 #ifdef _X86_
 typedef FLOATING_SAVE_AREA $FloatingSaveArea;
diff --git a/src/pkg/runtime/windows/thread.c b/src/pkg/runtime/windows/thread.c
index 97a42d73a0f..ff075b77dce 100644
--- a/src/pkg/runtime/windows/thread.c
+++ b/src/pkg/runtime/windows/thread.c
@@ -17,6 +17,7 @@
 #pragma dynimport runtime·GetEnvironmentStringsW GetEnvironmentStringsW "kernel32.dll"
 #pragma dynimport runtime·GetProcAddress GetProcAddress "kernel32.dll"
 #pragma dynimport runtime·GetStdHandle GetStdHandle "kernel32.dll"
+#pragma dynimport runtime·GetSystemInfo GetSystemInfo "kernel32.dll"
 #pragma dynimport runtime·GetThreadContext GetThreadContext "kernel32.dll"
 #pragma dynimport runtime·LoadLibraryEx LoadLibraryExA "kernel32.dll"
 #pragma dynimport runtime·QueryPerformanceCounter QueryPerformanceCounter "kernel32.dll"
@@ -26,6 +27,7 @@
 #pragma dynimport runtime·SetEvent SetEvent "kernel32.dll"
 #pragma dynimport runtime·SetThreadPriority SetThreadPriority "kernel32.dll"
 #pragma dynimport runtime·SetWaitableTimer SetWaitableTimer "kernel32.dll"
+#pragma dynimport runtime·Sleep Sleep "kernel32.dll"
 #pragma dynimport runtime·SuspendThread SuspendThread "kernel32.dll"
 #pragma dynimport runtime·timeBeginPeriod timeBeginPeriod "winmm.dll"
 #pragma dynimport runtime·WaitForSingleObject WaitForSingleObject "kernel32.dll"
@@ -41,6 +43,7 @@ extern void *runtime·FreeEnvironmentStringsW;
 extern void *runtime·GetEnvironmentStringsW;
 extern void *runtime·GetProcAddress;
 extern void *runtime·GetStdHandle;
+extern void *runtime·GetSystemInfo;
 extern void *runtime·GetThreadContext;
 extern void *runtime·LoadLibraryEx;
 extern void *runtime·QueryPerformanceCounter;
@@ -50,6 +53,7 @@ extern void *runtime·SetConsoleCtrlHandler;
 extern void *runtime·SetEvent;
 extern void *runtime·SetThreadPriority;
 extern void *runtime·SetWaitableTimer;
+extern void *runtime·Sleep;
 extern void *runtime·SuspendThread;
 extern void *runtime·timeBeginPeriod;
 extern void *runtime·WaitForSingleObject;
@@ -57,6 +61,15 @@ extern void *runtime·WriteFile;
 
 static int64 timerfreq;
 
+static int32
+getproccount(void)
+{
+	SystemInfo info;
+
+	runtime·stdcall(runtime·GetSystemInfo, 1, &info);
+	return info.dwNumberOfProcessors;
+}
+
 void
 runtime·osinit(void)
 {
@@ -67,6 +80,7 @@ runtime·osinit(void)
 	runtime·stdcall(runtime·QueryPerformanceFrequency, 1, &timerfreq);
 	runtime·stdcall(runtime·SetConsoleCtrlHandler, 2, runtime·ctrlhandler, (uintptr)1);
 	runtime·stdcall(runtime·timeBeginPeriod, 1, (uintptr)1);
+	runtime·ncpu = getproccount();
 }
 
 void
@@ -126,6 +140,21 @@ runtime·write(int32 fd, void *buf, int32 n)
 	return written;
 }
 
+void
+runtime·osyield(void)
+{
+	runtime·stdcall(runtime·Sleep, 1, (uintptr)0);
+}
+
+void
+runtime·usleep(uint32 us)
+{
+	us /= 1000;
+	if(us == 0)
+		us = 1;
+	runtime·stdcall(runtime·Sleep, 1, (uintptr)us);
+}
+
 // Thread-safe allocation of an event.
 static void
 initevent(void **pevent)