diff --git a/noise/basis/perlin.hpp b/noise/basis/perlin.hpp
index 2f15513c..e0baabdc 100644
--- a/noise/basis/perlin.hpp
+++ b/noise/basis/perlin.hpp
@@ -30,7 +30,7 @@ namespace util { namespace noise { namespace basis {
         perlin ();
 
         range<T> bounds (void) const;
-        T operator() (point<2,T>) const;
+        constexpr T operator() (point<2,T>) const;
 
         seed_t seed;
 
diff --git a/noise/basis/perlin.ipp b/noise/basis/perlin.ipp
index 2e151847..7265cc1c 100644
--- a/noise/basis/perlin.ipp
+++ b/noise/basis/perlin.ipp
@@ -50,7 +50,7 @@ namespace util { namespace noise { namespace basis {
 
     //-------------------------------------------------------------------------
     template <typename T, util::noise::lerp_t<T> L>
-    T
+    constexpr T
     perlin<T,L>::operator() (util::point<2,T> p) const
     {
         // extract integer and fractional parts. be careful to always round down
diff --git a/noise/basis/value.hpp b/noise/basis/value.hpp
index b7c4016e..b02a8297 100644
--- a/noise/basis/value.hpp
+++ b/noise/basis/value.hpp
@@ -30,7 +30,7 @@ namespace util { namespace noise { namespace basis {
         value ();
 
         range<T> bounds (void) const;
-        T operator() (util::point<2,T>) const;
+        constexpr T operator() (util::point<2,T>) const;
 
         seed_t seed;
 
diff --git a/noise/basis/value.ipp b/noise/basis/value.ipp
index fbde6e5a..698b667e 100644
--- a/noise/basis/value.ipp
+++ b/noise/basis/value.ipp
@@ -47,7 +47,7 @@ namespace util { namespace noise { namespace basis {
 
     //-------------------------------------------------------------------------
     template <typename T, util::noise::lerp_t<T> L>
-    T
+    constexpr T
     value<T,L>::operator() (util::point<2,T> p) const
     {
         // extract integer and fractional parts. be careful to always round down
diff --git a/noise/basis/worley.hpp b/noise/basis/worley.hpp
index 47755c70..add2a95f 100644
--- a/noise/basis/worley.hpp
+++ b/noise/basis/worley.hpp
@@ -29,7 +29,7 @@ namespace util { namespace noise { namespace basis {
         worley ();
 
         range<T> bounds (void) const;
-        T operator() (util::point<2,T>) const;
+        constexpr T operator() (util::point<2,T>) const;
 
         seed_t seed;
 
diff --git a/noise/basis/worley.ipp b/noise/basis/worley.ipp
index f0969d9f..132fe8b2 100644
--- a/noise/basis/worley.ipp
+++ b/noise/basis/worley.ipp
@@ -50,7 +50,7 @@ namespace util { namespace noise { namespace basis {
 
     //-------------------------------------------------------------------------
     template <typename T, size_t F>
-    T
+    constexpr T
     worley<T,F>::operator() (util::point<2,T> p) const
     {
         // extract integer and fractional parts. be careful to always round down
@@ -61,8 +61,8 @@ namespace util { namespace noise { namespace basis {
         auto p_rem = abs (p - p_int).template as<point> ();
 
         // setup an array of distances
-        static constexpr size_t RADIUS = 1;
-        static constexpr size_t COUNT = pow2 (RADIUS * 2 + 1);
+        constexpr size_t RADIUS = 1;
+        constexpr size_t COUNT = pow2 (RADIUS * 2 + 1);
         T distances[COUNT] = { std::numeric_limits<T>::quiet_NaN () };
         T *cursor = distances;
 
diff --git a/noise/fractal/fbm.hpp b/noise/fractal/fbm.hpp
index 5b2f337c..6c370e24 100644
--- a/noise/fractal/fbm.hpp
+++ b/noise/fractal/fbm.hpp
@@ -60,7 +60,7 @@ namespace util { namespace noise { namespace fractal {
         T gain;
 
         B basis;
-        T operator() (util::point<2,T>) const;
+        constexpr T operator() (util::point<2,T>) const;
     };
 } } }
 
diff --git a/noise/fractal/fbm.ipp b/noise/fractal/fbm.ipp
index 474de734..8a81f3bd 100644
--- a/noise/fractal/fbm.ipp
+++ b/noise/fractal/fbm.ipp
@@ -58,7 +58,7 @@ namespace util { namespace noise { namespace fractal {
 
     //-------------------------------------------------------------------------
     template <typename T, typename B>
-    T
+    constexpr T
     fbm<T,B>::operator() (util::point<2,T> p) const
     {
         T total = 0;
diff --git a/noise/fractal/hetero.hpp b/noise/fractal/hetero.hpp
index d84914d8..bc238e89 100644
--- a/noise/fractal/hetero.hpp
+++ b/noise/fractal/hetero.hpp
@@ -44,7 +44,7 @@ namespace util { namespace noise { namespace fractal {
 
         B basis;
 
-        T operator() (util::point<2,T>) const;
+        constexpr T operator() (util::point<2,T>) const;
     };
 } } }
 
diff --git a/noise/fractal/hetero.ipp b/noise/fractal/hetero.ipp
index 648f0c39..a0928de3 100644
--- a/noise/fractal/hetero.ipp
+++ b/noise/fractal/hetero.ipp
@@ -35,7 +35,7 @@ namespace util { namespace noise { namespace fractal {
 
     //-------------------------------------------------------------------------
     template <typename T, typename B>
-    T
+    constexpr T
     hetero<T,B>::operator() (util::point<2,T> p) const
     {
         T exponents[octaves];
diff --git a/noise/fractal/hmf.hpp b/noise/fractal/hmf.hpp
index 06f482ce..1b627f41 100644
--- a/noise/fractal/hmf.hpp
+++ b/noise/fractal/hmf.hpp
@@ -44,7 +44,7 @@ namespace util { namespace noise { namespace fractal {
 
         B basis;
 
-        T operator() (util::point<2,T>) const;
+        constexpr T operator() (util::point<2,T>) const;
     };
 } } }
 
diff --git a/noise/fractal/hmf.ipp b/noise/fractal/hmf.ipp
index 9b3d1219..3b623ea4 100644
--- a/noise/fractal/hmf.ipp
+++ b/noise/fractal/hmf.ipp
@@ -36,7 +36,7 @@ namespace util { namespace noise { namespace fractal {
 
     //-------------------------------------------------------------------------
     template <typename T, typename B>
-    T
+    constexpr T
     hmf<T,B>::operator() (util::point<2,T> p) const
     {
         T exponents[octaves];
diff --git a/noise/fractal/rmf.hpp b/noise/fractal/rmf.hpp
index 7c3c6ab7..90c11d95 100644
--- a/noise/fractal/rmf.hpp
+++ b/noise/fractal/rmf.hpp
@@ -55,7 +55,7 @@ namespace util { namespace noise { namespace fractal {
         T gain;
 
         B basis;
-        T operator() (util::point<2,T>) const;
+        constexpr T operator() (util::point<2,T>) const;
     };
 } } }
 
diff --git a/noise/fractal/rmf.ipp b/noise/fractal/rmf.ipp
index b15bccec..f8f1c87c 100644
--- a/noise/fractal/rmf.ipp
+++ b/noise/fractal/rmf.ipp
@@ -53,7 +53,7 @@ namespace util { namespace noise { namespace fractal {
 
     //-------------------------------------------------------------------------
     template <typename T, typename B>
-    T
+    constexpr T
     rmf<T,B>::operator() (util::point<2,T> p) const
     {
         const T offset = 1;