diff -up ./QGLViewer/vec.h.qreal ./QGLViewer/vec.h
--- ./QGLViewer/vec.h.qreal	2016-10-06 16:08:49.000000000 -0400
+++ ./QGLViewer/vec.h	2018-08-12 11:13:30.254206103 -0400
@@ -168,12 +168,20 @@ public:
   glNormal3dv(normal);
   glVertex3dv(pos);
   \endcode */
-	operator const qreal*() const {
+	operator const double*() const {
+		if (sizeof(x) == sizeof(double)) {
 #ifdef QGLVIEWER_UNION_NOT_SUPPORTED
-		return &x;
+			return (double*)&x;
 #else
-		return v_;
+			return (double*)v_;
 #endif
+		} else {
+			static double* const result = new double[3];
+			result[0] = static_cast<double>(x);
+			result[1] = static_cast<double>(y);
+			result[2] = static_cast<double>(z);
+			return result;
+		}
 	}
 
 	/*! Non const conversion operator returning the memory address of the vector.
@@ -197,11 +205,19 @@ public:
   \endcode
   \note The returned float array is a static shared by all \c Vec instances. */
 	operator const float*() const {
-		static float* const result = new float[3];
-		result[0] = (float)x;
-		result[1] = (float)y;
-		result[2] = (float)z;
-		return result;
+		if (std::is_same<double, qreal>::value) {
+		static float* const result = new float[3];
+			result[0] = static_cast<float>(x);
+			result[1] = static_cast<float>(y);
+			result[2] = static_cast<float>(z);
+			return result;
+		} else {
+#ifdef QGLVIEWER_UNION_NOT_SUPPORTED
+			return (float*)&x;
+#else
+			return (float*)v_;
+#endif
+		}
 	}
 	//@}