diff --git a/extent.hpp b/extent.hpp
index 867e93b0..d3587b03 100644
--- a/extent.hpp
+++ b/extent.hpp
@@ -166,13 +166,17 @@ namespace cruft {
     }
 
 
+    /// Return a uniform random point that lies within the extent.
+    ///
+    /// The interval conventions are the same as for the std library; close for
+    /// integers, half-open for reals.
     template <size_t S, typename T, typename GeneratorT>
     cruft::point<S,T>
     sample (cruft::extent<S,T> shape, GeneratorT &&gen)
     {
         cruft::point<S,T> p;
         for (size_t i = 0; i < S; ++i)
-            p[i] = cruft::random::uniform (0, shape[i], gen);
+            p[i] = cruft::random::uniform (T{0}, shape[i], gen);
         return p;
     }