diff --git a/configure.py b/configure.py
index cc5846d4..a8abb782 100755
--- a/configure.py
+++ b/configure.py
@@ -41,6 +41,7 @@ COMPLETE_OBJECTS = [
     "Kyoto/Math/CVector3d",
     "Kyoto/Math/CVector3i",
     "Kyoto/Math/CloseEnough",
+    "Kyoto/Math/CSphere",
     "Kyoto/CRandom16",
     "Kyoto/CCrc32",
     "Kyoto/Alloc/CCircularBuffer",
diff --git a/include/Kyoto/Math/CSphere.hpp b/include/Kyoto/Math/CSphere.hpp
index cb206eaf..e925a2e5 100644
--- a/include/Kyoto/Math/CSphere.hpp
+++ b/include/Kyoto/Math/CSphere.hpp
@@ -4,12 +4,13 @@
 #include "types.h"
 
 #include "Kyoto/Math/CVector3f.hpp"
+#include "Kyoto/Math/CUnitVector3f.hpp"
 
 class CSphere {
 public:
   CSphere(const CVector3f& pos, f32 radius) : x0_pos(pos), xc_radius(radius) {}
 
-  // TODO
+  CUnitVector3f GetSurfaceNormal(const CVector3f& v) const;
 
 private:
   CVector3f x0_pos;
diff --git a/obj_files.mk b/obj_files.mk
index e12aa592..7a9d3473 100644
--- a/obj_files.mk
+++ b/obj_files.mk
@@ -544,7 +544,7 @@ KYOTO_1 :=\
 	$(BUILD_DIR)/asm/Kyoto/Particles/CVectorElement.o\
 	$(BUILD_DIR)/src/Kyoto/Particles/CWarp.o\
 	$(BUILD_DIR)/src/Kyoto/Math/CPlane.o\
-	$(BUILD_DIR)/asm/Kyoto/Math/CSphere.o\
+	$(BUILD_DIR)/src/Kyoto/Math/CSphere.o\
 	$(BUILD_DIR)/asm/Kyoto/Math/CAABox.o\
 	$(BUILD_DIR)/asm/Kyoto/CFactoryMgr.o\
 	$(BUILD_DIR)/asm/Kyoto/CResFactory.o\
diff --git a/src/Kyoto/Math/CSphere.cpp b/src/Kyoto/Math/CSphere.cpp
new file mode 100644
index 00000000..e9c6d470
--- /dev/null
+++ b/src/Kyoto/Math/CSphere.cpp
@@ -0,0 +1,5 @@
+#include "Kyoto/Math/CSphere.hpp"
+
+CUnitVector3f CSphere::GetSurfaceNormal(const CVector3f& vec) const {
+  return CUnitVector3f(vec - x0_pos);
+}