diff --git a/src/qir/ast/expression/QIRNull.java b/src/qir/ast/expression/QIRNull.java
index df1a69de5622a21095afb33a25444a54355b014b..c496eeb117d2c994080b0b6f340db94f66c8ab9d 100644
--- a/src/qir/ast/expression/QIRNull.java
+++ b/src/qir/ast/expression/QIRNull.java
@@ -14,7 +14,11 @@ public final class QIRNull extends QIRBaseValue<Void> {
     /**
      * The unique representation of the {@code null} value.
      */
-    public static final QIRNull instance = new QIRNull();
+    private static final QIRNull instance = new QIRNull();
+
+    public static final QIRNull getInstance() {
+        return instance;
+    }
 
     @Override
     public final String toString() {
diff --git a/src/qir/driver/sql/SQLStringDriver.java b/src/qir/driver/sql/SQLStringDriver.java
index 608db88cba80214caa5253bf7fe27628959828ad..351b54d05fecb4967f5c0cedf077ef52985b7927 100644
--- a/src/qir/driver/sql/SQLStringDriver.java
+++ b/src/qir/driver/sql/SQLStringDriver.java
@@ -64,7 +64,7 @@ abstract class SQLStringDriver extends SQLDriver<String> {
                             data = new QIRDouble(null, rs.getDouble(i));
                             break;
                         case Types.NULL:
-                            data = QIRNull.instance;
+                            data = QIRNull.getInstance();
                             break;
                         case Types.OTHER:
                             String v = rs.getString(i);