diff --git a/src/graphics/opengl/gl21device.cpp b/src/graphics/opengl/gl21device.cpp
index aacfc31d..a64b326d 100644
--- a/src/graphics/opengl/gl21device.cpp
+++ b/src/graphics/opengl/gl21device.cpp
@@ -429,7 +429,7 @@ void CGL21Device::SetTransform(TransformType type, const Math::Matrix &matrix)
         // normal transform
         Math::Matrix normalMat = matrix;
 
-        if (abs(normalMat.Det()) > 1e-6)
+        if (fabs(normalMat.Det()) > 1e-6)
             normalMat = normalMat.Inverse();
 
         glUniformMatrix4fv(uni_NormalMatrix, 1, GL_TRUE, normalMat.Array());
diff --git a/src/graphics/opengl/gl33device.cpp b/src/graphics/opengl/gl33device.cpp
index f15625f7..b27b4cb6 100644
--- a/src/graphics/opengl/gl33device.cpp
+++ b/src/graphics/opengl/gl33device.cpp
@@ -456,7 +456,7 @@ void CGL33Device::SetTransform(TransformType type, const Math::Matrix &matrix)
         // normal transform
         Math::Matrix normalMat = matrix;
 
-        if (abs(normalMat.Det()) > 1e-6)
+        if (fabs(normalMat.Det()) > 1e-6)
             normalMat = normalMat.Inverse();
 
         glUniformMatrix4fv(uni_NormalMatrix, 1, GL_TRUE, normalMat.Array());