diff --git a/java/src/org/broadinstitute/sting/utils/genotype/vcf/VCFGenotypeWriterAdapter.java b/java/src/org/broadinstitute/sting/utils/genotype/vcf/VCFGenotypeWriterAdapter.java
index 3f38a53c0..98b89a0ec 100644
--- a/java/src/org/broadinstitute/sting/utils/genotype/vcf/VCFGenotypeWriterAdapter.java
+++ b/java/src/org/broadinstitute/sting/utils/genotype/vcf/VCFGenotypeWriterAdapter.java
@@ -203,7 +203,7 @@ public class VCFGenotypeWriterAdapter implements GenotypeWriter {
                 }
                 this.referenceBase = refBase;
             } else {
-                if (contig.equals(this.contig))
+                if (!contig.equals(this.contig))
                     throw new IllegalArgumentException("The contig name has to be the same at a single locus");
                 if (position != this.position)
                     throw new IllegalArgumentException("The position has to be the same at a single locus");