diff --git a/reactos/dll/directx/wine/d3dx9_36/CMakeLists.txt b/reactos/dll/directx/wine/d3dx9_36/CMakeLists.txt
index 60b442368d8..ec30fa48599 100644
--- a/reactos/dll/directx/wine/d3dx9_36/CMakeLists.txt
+++ b/reactos/dll/directx/wine/d3dx9_36/CMakeLists.txt
@@ -1,5 +1,5 @@
 
-add_definitions(-D__WINESRC__)
+add_definitions(-D__WINESRC__ -Dcopysignf=_copysignf)
 include_directories(${REACTOS_SOURCE_DIR}/include/reactos/wine)
 spec2def(d3dx9_36.dll d3dx9_36.spec ADD_IMPORTLIB)
 
diff --git a/reactos/dll/directx/wine/d3dx9_36/math.c b/reactos/dll/directx/wine/d3dx9_36/math.c
index 2229cb4f849..910e4f9377d 100644
--- a/reactos/dll/directx/wine/d3dx9_36/math.c
+++ b/reactos/dll/directx/wine/d3dx9_36/math.c
@@ -2118,7 +2118,7 @@ unsigned short float_32_to_16(const float in)
 {
     int exp = 0, origexp;
     float tmp = fabsf(in);
-    int sign = (in < 0);
+    int sign = (copysignf(1, in) < 0);
     unsigned int mantissa;
     unsigned short ret;
 
diff --git a/reactos/dll/directx/wine/wined3d/CMakeLists.txt b/reactos/dll/directx/wine/wined3d/CMakeLists.txt
index d1192c7781b..d0527b2bd5a 100644
--- a/reactos/dll/directx/wine/wined3d/CMakeLists.txt
+++ b/reactos/dll/directx/wine/wined3d/CMakeLists.txt
@@ -2,7 +2,8 @@
 add_definitions(
     -D__WINESRC__
     -D_USE_MATH_DEFINES
-    -DUSE_WIN32_OPENGL)
+    -DUSE_WIN32_OPENGL
+    -Dcopysignf=_copysignf)
 
 include_directories(BEFORE ${REACTOS_SOURCE_DIR}/include/reactos/wine)
 
diff --git a/reactos/dll/directx/wine/wined3d/utils.c b/reactos/dll/directx/wine/wined3d/utils.c
index e7b56ce5237..721548524e3 100644
--- a/reactos/dll/directx/wine/wined3d/utils.c
+++ b/reactos/dll/directx/wine/wined3d/utils.c
@@ -3987,7 +3987,7 @@ void wined3d_ftoa(float value, char *s)
 {
     int idx = 1;
 
-    if (value < 0.0f)
+    if (copysignf(1.0f, value) < 0.0f)
         ++idx;
 
     /* Be sure to allocate a buffer of at least 17 characters for the result