diff --git a/src/main/java/org/apache/commons/math/linear/IterativeLinearSolver.java b/src/main/java/org/apache/commons/math/linear/IterativeLinearSolver.java
index 70e74ec8b..fb5d7f61f 100644
--- a/src/main/java/org/apache/commons/math/linear/IterativeLinearSolver.java
+++ b/src/main/java/org/apache/commons/math/linear/IterativeLinearSolver.java
@@ -88,10 +88,10 @@ public abstract class IterativeLinearSolver {
         }
         if (inPlace) {
             MathUtils.checkNotNull(x0);
-            if (x0.getDimension() != a.getColumnDimension()) {
-                throw new DimensionMismatchException(x0.getDimension(),
-                                                     a.getColumnDimension());
-            }
+        }
+        if ((x0 != null) && (x0.getDimension() != a.getColumnDimension())) {
+            throw new DimensionMismatchException(x0.getDimension(),
+                                                 a.getColumnDimension());
         }
     }
 
diff --git a/src/main/java/org/apache/commons/math/linear/PreconditionedIterativeLinearSolver.java b/src/main/java/org/apache/commons/math/linear/PreconditionedIterativeLinearSolver.java
index e2514c283..f75b268a1 100644
--- a/src/main/java/org/apache/commons/math/linear/PreconditionedIterativeLinearSolver.java
+++ b/src/main/java/org/apache/commons/math/linear/PreconditionedIterativeLinearSolver.java
@@ -126,10 +126,10 @@ public abstract class PreconditionedIterativeLinearSolver
     /** {@inheritDoc} */
     @Override
     public RealVector solve(final RealLinearOperator a, final RealVector b,
-                            final RealVector x, final boolean inPlace)
+                            final RealVector x0, final boolean inPlace)
         throws NullArgumentException, NonSquareLinearOperatorException,
         DimensionMismatchException, MaxCountExceededException {
-        checkParameters(a, b, x, inPlace);
-        return solve(a, null, b, x, inPlace);
+        checkParameters(a, b, x0, inPlace);
+        return solve(a, null, b, x0, inPlace);
     }
 }