diff --git a/jsql/src/main/java/org/jaxdb/jsql/ComparisonPredicate.java b/jsql/src/main/java/org/jaxdb/jsql/ComparisonPredicate.java
index 9bbb2adc..a16677b9 100644
--- a/jsql/src/main/java/org/jaxdb/jsql/ComparisonPredicate.java
+++ b/jsql/src/main/java/org/jaxdb/jsql/ComparisonPredicate.java
@@ -62,7 +62,7 @@ static class Eq<V> extends LogicalPredicate<V> {
 
     @Override
     final StringBuilder compile(final Compiler compiler, final StringBuilder b, final boolean isForUpdateWhere) {
-      return b.append('=');
+      return b.append(this.b == null ? "IS" : "=");
     }
   }
 
@@ -85,7 +85,7 @@ static class Ne<V> extends LogicalPredicate<V> {
 
     @Override
     final StringBuilder compile(final Compiler compiler, final StringBuilder b, final boolean isForUpdateWhere) {
-      return b.append("!=");
+      return b.append(this.b == null ? "IS NOT" : "!=");
     }
   }
 
@@ -108,6 +108,7 @@ static class Gt<V> extends LogicalPredicate<V> {
 
     @Override
     final StringBuilder compile(final Compiler compiler, final StringBuilder b, final boolean isForUpdateWhere) {
+      super.compile(compiler, b, isForUpdateWhere);
       return b.append('>');
     }
   }
@@ -131,6 +132,7 @@ static class Lt<V> extends LogicalPredicate<V> {
 
     @Override
     final StringBuilder compile(final Compiler compiler, final StringBuilder b, final boolean isForUpdateWhere) {
+      super.compile(compiler, b, isForUpdateWhere);
       return b.append('<');
     }
   }
@@ -154,6 +156,7 @@ static class Gte<V> extends LogicalPredicate<V> {
 
     @Override
     final StringBuilder compile(final Compiler compiler, final StringBuilder b, final boolean isForUpdateWhere) {
+      super.compile(compiler, b, isForUpdateWhere);
       return b.append(">=");
     }
   }
@@ -177,6 +180,7 @@ static class Lte<V> extends LogicalPredicate<V> {
 
     @Override
     final StringBuilder compile(final Compiler compiler, final StringBuilder b, final boolean isForUpdateWhere) {
+      super.compile(compiler, b, isForUpdateWhere);
       return b.append("<=");
     }
   }
@@ -184,7 +188,7 @@ final StringBuilder compile(final Compiler compiler, final StringBuilder b, fina
   private ComparisonPredicate(final type.Column<?> a, final V b) {
     super(((Subject)a).getTable());
     this.a = (Subject)a;
-    this.b = org.jaxdb.jsql.data.wrap(b);
+    this.b = b == null ? null : org.jaxdb.jsql.data.wrap(b);
   }
 
   private ComparisonPredicate(final type.Column<?> a, final QuantifiedComparisonPredicate<?> b) {
@@ -195,7 +199,7 @@ private ComparisonPredicate(final type.Column<?> a, final QuantifiedComparisonPr
 
   private ComparisonPredicate(final V a, final type.Column<?> b) {
     super(((Subject)b).getTable());
-    this.a = org.jaxdb.jsql.data.wrap(a);
+    this.a = a == null ? null : org.jaxdb.jsql.data.wrap(a);
     this.b = (Subject)b;
   }
 
@@ -221,4 +225,12 @@ final void collectColumns(final ArrayList<data.Column<?>> list) {
     collectColumn(list, a);
     collectColumn(list, b);
   }
+
+  @Override
+  StringBuilder compile(final Compiler compiler, final StringBuilder b, final boolean isForUpdateWhere) {
+    if (b == null)
+      throw new IllegalArgumentException("NULL is not allowed for " + this.getClass().getSimpleName());
+
+    return null;
+  }
 }
\ No newline at end of file
diff --git a/jsql/src/main/java/org/jaxdb/jsql/Compiler.java b/jsql/src/main/java/org/jaxdb/jsql/Compiler.java
index 39498fa7..b751039b 100644
--- a/jsql/src/main/java/org/jaxdb/jsql/Compiler.java
+++ b/jsql/src/main/java/org/jaxdb/jsql/Compiler.java
@@ -811,6 +811,9 @@ void compilePredicate(final ComparisonPredicate<?> predicate, final Compilation
         unwrapAlias(predicate.a).compile(compilation, true);
         sql.append(')');
       }
+      else if (predicate.a == null) {
+        throw new IllegalArgumentException("lhs is NULL");
+      }
       else {
         unwrapAlias(predicate.a).compile(compilation, true);
       }
@@ -835,6 +838,9 @@ void compilePredicate(final ComparisonPredicate<?> predicate, final Compilation
         unwrapAlias(predicate.b).compile(compilation, true);
         sql.append(')');
       }
+      else if (predicate.b == null) {
+        compilation.sql.append("NULL");
+      }
       else {
         unwrapAlias(predicate.b).compile(compilation, true);
       }
diff --git a/jsql/src/main/java/org/jaxdb/jsql/PostgreSQLCompiler.java b/jsql/src/main/java/org/jaxdb/jsql/PostgreSQLCompiler.java
index ba070944..aa6b0b24 100644
--- a/jsql/src/main/java/org/jaxdb/jsql/PostgreSQLCompiler.java
+++ b/jsql/src/main/java/org/jaxdb/jsql/PostgreSQLCompiler.java
@@ -270,12 +270,14 @@ private static void toChar(final data.ENUM<?> column, final Compilation compilat
   final void compilePredicate(final ComparisonPredicate<?> predicate, final Compilation compilation) throws IOException, SQLException {
     final Subject a = predicate.a;
     final Subject b = predicate.b;
-    if (a.getClass() == b.getClass() || (!(a instanceof data.ENUM) && !(b instanceof data.ENUM))) {
+    if (!(a instanceof data.ENUM) && !(b instanceof data.ENUM) || (a != null && b != null && a.getClass() == b.getClass())) {
       super.compilePredicate(predicate, compilation);
     }
     else {
       if (a instanceof data.ENUM)
         toChar((data.ENUM<?>)a, compilation);
+      else if (a == null)
+        compilation.sql.append("NULL");
       else
         a.compile(compilation, true);
 
@@ -285,6 +287,8 @@ final void compilePredicate(final ComparisonPredicate<?> predicate, final Compil
       sql.append(' ');
       if (b instanceof data.ENUM)
         toChar((data.ENUM<?>)b, compilation);
+      else if (b == null)
+        compilation.sql.append("NULL");
       else
         b.compile(compilation, true);
     }