diff --git a/test/triqs/gfs/gf_notail.cpp b/test/triqs/gfs/gf_notail.cpp
index 46944b00..80532990 100644
--- a/test/triqs/gfs/gf_notail.cpp
+++ b/test/triqs/gfs/gf_notail.cpp
@@ -32,7 +32,18 @@ int main() {
   // rebuilding a new gf...
   auto g3 = make_gf_from_g_and_tail(vw, gw.singularity());
   // need to test all this....
-  
+ 
+  //test antiperiodicity
+  auto Gt = gf<imtime, scalar_valued, no_tail>{ { beta, Fermion, 1000 }, {  } };
+  Gt(tau_) << exp(-tau_);
+
+  TEST(Gt(0.01));
+  TEST(Gt(.5));
+  TEST(Gt(.9));
+  TEST(Gt(-.1));//should be equal to line above
+
+
+
  }
  TRIQS_CATCH_AND_ABORT;
 }
diff --git a/test/triqs/gfs/gf_notail.output b/test/triqs/gfs/gf_notail.output
new file mode 100644
index 00000000..9988d894
--- /dev/null
+++ b/test/triqs/gfs/gf_notail.output
@@ -0,0 +1,8 @@
+(Gt(0.01)) ---> 0.99005
+
+(Gt(.5)) ---> 0.606531
+
+(Gt(.9)) ---> 0.40657
+
+(Gt(-.1)) ---> -0.40657
+
diff --git a/triqs/gfs/imtime.hpp b/triqs/gfs/imtime.hpp
index f760e048..ed7c38a0 100644
--- a/triqs/gfs/imtime.hpp
+++ b/triqs/gfs/imtime.hpp
@@ -84,6 +84,7 @@ namespace gfs {
     double w;
     bool in;
     std::tie(in, n, w) = windowing(m, tau);
+    if (!in) TRIQS_RUNTIME_ERROR << " Evaluation out of bounds";
     if ((m.domain().statistic == Fermion) && (p % 2 != 0)) {
      w2 = -w;
      w1 = w - 1;