diff --git a/tetrad-lib/src/main/java/edu/cmu/tetrad/data/CovariancesDoubleForkJoin.java b/tetrad-lib/src/main/java/edu/cmu/tetrad/data/CovariancesDoubleForkJoin.java
index fd4ecee038..c9e31addca 100644
--- a/tetrad-lib/src/main/java/edu/cmu/tetrad/data/CovariancesDoubleForkJoin.java
+++ b/tetrad-lib/src/main/java/edu/cmu/tetrad/data/CovariancesDoubleForkJoin.java
@@ -49,6 +49,10 @@ public CovariancesDoubleForkJoin(double[][] data, boolean biasCorrected) {
             numThreads /= 2;
         }
 
+        if (numThreads < 1) {
+            numThreads = 1;
+        }
+
         RealCovarianceMatrixForkJoin cov = new RealCovarianceMatrixForkJoin(data, numThreads);
         this.covariances = cov.compute(biasCorrected);
     }