diff --git a/simgear/math/SGVec2.hxx b/simgear/math/SGVec2.hxx
index 87c6fe2f..f7f97550 100644
--- a/simgear/math/SGVec2.hxx
+++ b/simgear/math/SGVec2.hxx
@@ -406,7 +406,6 @@ point_in_triangle(const SGVec2<T>& testpt, const SGVec2<T>& pt1, const SGVec2<T>
   return !(has_neg && has_pos);
 }
 
-#ifndef NDEBUG
 template<typename T>
 inline
 bool
@@ -414,7 +413,6 @@ isNaN(const SGVec2<T>& v)
 {
   return SGMisc<T>::isNaN(v(0)) || SGMisc<T>::isNaN(v(1));
 }
-#endif
 
 /// Output to an ostream
 template<typename char_type, typename traits_type, typename T>
diff --git a/simgear/math/SGVec3.hxx b/simgear/math/SGVec3.hxx
index aa1061b8..ae03c02b 100644
--- a/simgear/math/SGVec3.hxx
+++ b/simgear/math/SGVec3.hxx
@@ -491,7 +491,6 @@ interpolate(T tau, const SGVec3<T>& v1, const SGVec3<T>& v2)
   return r;
 }
 
-#ifndef NDEBUG
 template<typename T>
 inline
 bool
@@ -500,7 +499,6 @@ isNaN(const SGVec3<T>& v)
   return SGMisc<T>::isNaN(v(0)) ||
     SGMisc<T>::isNaN(v(1)) || SGMisc<T>::isNaN(v(2));
 }
-#endif
 
 /// Output to an ostream
 template<typename char_type, typename traits_type, typename T>
diff --git a/simgear/math/SGVec4.hxx b/simgear/math/SGVec4.hxx
index bd66389f..9000c8c6 100644
--- a/simgear/math/SGVec4.hxx
+++ b/simgear/math/SGVec4.hxx
@@ -409,7 +409,6 @@ interpolate(T tau, const SGVec4<T>& v1, const SGVec4<T>& v2)
   return r;
 }
 
-#ifndef NDEBUG
 template<typename T>
 inline
 bool
@@ -418,7 +417,6 @@ isNaN(const SGVec4<T>& v)
   return SGMisc<T>::isNaN(v(0)) || SGMisc<T>::isNaN(v(1))
     || SGMisc<T>::isNaN(v(2)) || SGMisc<T>::isNaN(v(3));
 }
-#endif
 
 /// Output to an ostream
 template<typename char_type, typename traits_type, typename T>