diff --git a/src/Microsoft.ML.TimeSeries/FftUtils.cs b/src/Microsoft.ML.TimeSeries/FftUtils.cs
index 2b00009547..db5ac6ab11 100644
--- a/src/Microsoft.ML.TimeSeries/FftUtils.cs
+++ b/src/Microsoft.ML.TimeSeries/FftUtils.cs
@@ -248,7 +248,7 @@ public static void ComputeForwardFft(float[] inputRe, float[] inputIm, float[] o
             }
             finally
             {
-                if (descriptor != null)
+                if (descriptor != IntPtr.Zero)
                     FreeDescriptor(ref descriptor);
             }
         }
@@ -294,7 +294,7 @@ public static void ComputeBackwardFft(float[] inputRe, float[] inputIm, float[]
             }
             finally
             {
-                if (descriptor != null)
+                if (descriptor != IntPtr.Zero)
                     FreeDescriptor(ref descriptor);
             }
 
@@ -350,7 +350,7 @@ public static void ComputeForwardFft(double[] inputRe, double[] inputIm, double[
             }
             finally
             {
-                if (descriptor != null)
+                if (descriptor != IntPtr.Zero)
                     FreeDescriptor(ref descriptor);
             }
         }
@@ -396,7 +396,7 @@ public static void ComputeBackwardFft(double[] inputRe, double[] inputIm, double
             }
             finally
             {
-                if (descriptor != null)
+                if (descriptor != IntPtr.Zero)
                     FreeDescriptor(ref descriptor);
             }