diff --git a/src/main/java/ca/joeltherrien/randomforest/covariates/FactorCovariate.java b/src/main/java/ca/joeltherrien/randomforest/covariates/FactorCovariate.java
index cf48933..ebf6cf4 100644
--- a/src/main/java/ca/joeltherrien/randomforest/covariates/FactorCovariate.java
+++ b/src/main/java/ca/joeltherrien/randomforest/covariates/FactorCovariate.java
@@ -69,7 +69,7 @@ public final class FactorCovariate implements Covariate<String>{
 
     @Override
     public FactorValue createValue(String value) {
-        if(value == null){
+        if(value == null || value.equalsIgnoreCase("na")){
             return this.naValue;
         }
 
diff --git a/src/test/java/ca/joeltherrien/randomforest/csv/TestLoadingCSV.java b/src/test/java/ca/joeltherrien/randomforest/csv/TestLoadingCSV.java
index 5a1faf7..8032185 100644
--- a/src/test/java/ca/joeltherrien/randomforest/csv/TestLoadingCSV.java
+++ b/src/test/java/ca/joeltherrien/randomforest/csv/TestLoadingCSV.java
@@ -22,6 +22,7 @@ public class TestLoadingCSV {
         5,3.0,"mouse",true
         2,1.0,"dog",false
         9,1.5,"cat",true
+        -3,NA,NA,NA
      */
 
     @Test
@@ -41,7 +42,7 @@ public class TestLoadingCSV {
 
         final List<Row<Double>> data = Main.loadData(covariates, settings);
 
-        assertEquals(3, data.size());
+        assertEquals(4, data.size());
 
         Row<Double> row = data.get(0);
         assertEquals(5.0, (double)row.getResponse());
@@ -61,6 +62,12 @@ public class TestLoadingCSV {
         assertEquals("cat", row.getCovariateValue("x2").getValue());
         assertEquals(true, row.getCovariateValue("x3").getValue());
 
+        row = data.get(3);
+        assertEquals(-3.0, (double)row.getResponse());
+        assertEquals(true, row.getCovariateValue("x1").isNA());
+        assertEquals(true, row.getCovariateValue("x2").isNA());
+        assertEquals(true, row.getCovariateValue("x3").isNA());
+
     }
 
 }
diff --git a/src/test/resources/testCSV.csv b/src/test/resources/testCSV.csv
index ca1d181..7083420 100644
--- a/src/test/resources/testCSV.csv
+++ b/src/test/resources/testCSV.csv
@@ -1,4 +1,5 @@
 y,x1,x2,x3
 5,3.0,"mouse",true
 2,1.0,"dog",false
-9,1.5,"cat",true
\ No newline at end of file
+9,1.5,"cat",true
+-3,NA,NA,NA
\ No newline at end of file