diff --git a/src/QLNet/Math/Interpolations/MixedInterpolation.cs b/src/QLNet/Math/Interpolations/MixedInterpolation.cs
index f7ce9ef7..19eeabcb 100644
--- a/src/QLNet/Math/Interpolations/MixedInterpolation.cs
+++ b/src/QLNet/Math/Interpolations/MixedInterpolation.cs
@@ -56,7 +56,7 @@ public MixedInterpolationImpl(List<double> xBegin, int xEnd,
          xBegin2_ = xBegin.GetRange(n_, xBegin.Count - n_);
          yBegin2_ = yBegin.GetRange(n_, yBegin.Count - n_);
 
-         Utils.QL_REQUIRE(xBegin2_.Count < size_, () => "too large n (" + n + ") for " + size_ + "-element x sequence");
+         Utils.QL_REQUIRE(xBegin2_.Count < xBegin.Count, () => "too large n (" + n + ") for " + size_ + "-element x sequence");
 
          switch (behavior)
          {
@@ -65,8 +65,16 @@ public MixedInterpolationImpl(List<double> xBegin, int xEnd,
                interpolation2_ = factory2.interpolate(xBegin_, size_, yBegin_);
                break;
             case Behavior.SplitRanges:
-               interpolation1_ = factory1.interpolate(xBegin_, n_, yBegin_);
-               interpolation2_ = factory2.interpolate(xBegin2_, size_ - n, yBegin2_);
+               if (size_ <= n_)
+               {
+                  interpolation1_ = factory1.interpolate(xBegin_, size_, yBegin_);
+                  interpolation2_ = interpolation1_;
+               }
+               else
+               {
+                  interpolation1_ = factory1.interpolate(xBegin_, n_, yBegin_);
+                  interpolation2_ = factory2.interpolate(xBegin2_, size_- n_, yBegin2_);
+               }
                break;
             default:
                Utils.QL_FAIL("unknown mixed-interpolation behavior: " + behavior);
@@ -83,14 +91,14 @@ public override void update()
 
       public override double value(double x)
       {
-         if (x<(xBegin2_.First()))
+         if (xBegin2_.Count == 0 || x < (xBegin2_.First()))
             return interpolation1_.value(x, true);
          return interpolation2_.value(x, true);
       }
 
       public override double primitive(double x)
       {
-         if (x<(xBegin2_.First()))
+         if (xBegin2_.Count == 0 || x < (xBegin2_.First()))
             return interpolation1_.primitive(x, true);
          return interpolation2_.primitive(x, true) -
                 interpolation2_.primitive(xBegin2_.First(), true) +
@@ -99,14 +107,14 @@ public override double primitive(double x)
 
       public override double derivative(double x)
       {
-         if (x < (xBegin2_.First()))
+         if (xBegin2_.Count == 0 || x < (xBegin2_.First()))
             return interpolation1_.derivative(x, true);
          return interpolation2_.derivative(x, true);
       }
 
       public override double secondDerivative(double x)
       {
-         if (x < (xBegin2_.First()))
+         if (xBegin2_.Count == 0 || x < (xBegin2_.First()))
             return interpolation1_.secondDerivative(x, true);
          return interpolation2_.secondDerivative(x, true);
       }