diff --git a/openjpa-jdbc/src/main/java/org/apache/openjpa/jdbc/kernel/StoredProcedureQuery.java b/openjpa-jdbc/src/main/java/org/apache/openjpa/jdbc/kernel/StoredProcedureQuery.java
index 93fb940798..dc52306710 100644
--- a/openjpa-jdbc/src/main/java/org/apache/openjpa/jdbc/kernel/StoredProcedureQuery.java
+++ b/openjpa-jdbc/src/main/java/org/apache/openjpa/jdbc/kernel/StoredProcedureQuery.java
@@ -186,15 +186,17 @@ public ResultObjectProvider executeQuery(StoreQuery q, Object[] params, Range ra
                 stmnt = conn.prepareCall(_proc.getCallSQL());
 
                 final StoredProcedureQuery spq = (StoredProcedureQuery) q;
+                // no parameter values at all: leave the (un)binding to the driver
+                final boolean bind = params != null && params.length > 0;
                 for (Column c : spq.getProcedure().getInColumns()) {
-                    if (params != null && c.getIndex() < params.length) {
+                    if (bind) {
                         dict.setUnknown(stmnt, c.getIndex() + 1, params[c.getIndex()], c);
                     }
                 }
                 for (Column c : spq.getProcedure().getInOutColumns()) {
                     final int index = c.getIndex() + 1;
                     stmnt.registerOutParameter(index, c.getType());
-                    if (params != null && index - 1 < params.length) {
+                    if (bind) {
                         dict.setUnknown(stmnt, index, params[index - 1], c);
                     }
                 }
@@ -265,21 +267,29 @@ public Object[] toParameterArray(StoreQuery q, Map<?, ?> userParams) {
             StoredProcedureQuery storedProcedureQuery = (StoredProcedureQuery) q;
             Column[] inCols = storedProcedureQuery.getProcedure().getInColumns();
             Column[] inOutCols = storedProcedureQuery.getProcedure().getInOutColumns();
-            int paramCount = inCols.length + inOutCols.length;
-            if (paramCount == 0) return NO_PARAM;
+            if (inCols.length + inOutCols.length == 0) return NO_PARAM;
+            // the values are indexed by the parameter position, OUT parameters leave a gap
+            int paramCount = 0;
+            for (final Column[] columns : asList(inCols, inOutCols)) {
+                for (Column c : columns) {
+                    paramCount = Math.max(paramCount, c.getIndex() + 1);
+                }
+            }
             Object[] array = new Object[paramCount];
-            int i = 0;
             for (final Column[] columns : asList(inCols, inOutCols)) {
                 for (Column c : columns) {
-                    // Try by name first, then by 1-based position (matching user's declaration)
-                    Object val = userParams.get(c.getIdentifier().getName());
-                    if (val == null) {
+                    // Try by name first, then by 1-based position (matching user's declaration).
+                    // An explicit null binding wins over a lookup by position.
+                    String name = c.getIdentifier().getName();
+                    Object val = null;
+                    if (userParams.containsKey(name)) {
+                        val = userParams.get(name);
+                    } else if (userParams.containsKey(c.getIndex() + 1)) {
                         val = userParams.get(c.getIndex() + 1);
-                    }
-                    if (val == null) {
+                    } else if (userParams.containsKey(c.getIndex())) {
                         val = userParams.get(c.getIndex());
                     }
-                    array[i++] = val;
+                    array[c.getIndex()] = val;
                 }
             }
             return array;
diff --git a/openjpa-persistence-jdbc/src/test/java/org/apache/openjpa/jdbc/procedure/TestStoredProcedureQueryFixes.java b/openjpa-persistence-jdbc/src/test/java/org/apache/openjpa/jdbc/procedure/TestStoredProcedureQueryFixes.java
index 4b0c9499e4..4fab54619b 100644
--- a/openjpa-persistence-jdbc/src/test/java/org/apache/openjpa/jdbc/procedure/TestStoredProcedureQueryFixes.java
+++ b/openjpa-persistence-jdbc/src/test/java/org/apache/openjpa/jdbc/procedure/TestStoredProcedureQueryFixes.java
@@ -186,6 +186,67 @@ public void testGetSingleResultNonUniqueResultException() throws Exception {
         }
     }
 
+    /**
+     * Test that a named parameter explicitly bound to null is not replaced by
+     * the value registered under the position of that parameter.
+     */
+    public void testExplicitNullNamedParameterWinsOverPosition() throws Exception {
+        Procedures.inParamsInteger = -1;
+        Procedures.inParamsString = null;
+
+        EntityManager em = emf.createEntityManager();
+        try {
+            exec(em, "DROP PROCEDURE TESTINS", true);
+            exec(em, "CREATE PROCEDURE TESTINS(SOME_NUMBER INTEGER,SOME_STRING VARCHAR(255)) " +
+                    "PARAMETER STYLE JAVA LANGUAGE JAVA EXTERNAL NAME " +
+                    "'" + Procedures.class.getName() + ".inParams'", false);
+
+            StoredProcedureQuery spq = em.createStoredProcedureQuery("TESTINS");
+            spq.registerStoredProcedureParameter("SOME_NUMBER", Integer.class, ParameterMode.IN);
+            spq.registerStoredProcedureParameter("SOME_STRING", String.class, ParameterMode.IN);
+            spq.registerStoredProcedureParameter(2, String.class, ParameterMode.IN);
+            spq.setParameter("SOME_NUMBER", 42);
+            spq.setParameter(2, "positional");
+            spq.setParameter("SOME_STRING", null);
+            assertFalse(spq.execute());
+
+            assertEquals(42, Procedures.inParamsInteger);
+            assertNull(Procedures.inParamsString);
+        } finally {
+            em.close();
+        }
+    }
+
+    /**
+     * Test that IN parameters following an OUT parameter are bound at their position.
+     */
+    public void testInParameterAfterOutParameter() throws Exception {
+        EntityManager em = emf.createEntityManager();
+        try {
+            exec(em, "DROP PROCEDURE XSUM", true);
+            exec(em, "CREATE PROCEDURE XSUM(IN A INTEGER,OUT S INTEGER,IN B INTEGER) " +
+                    "PARAMETER STYLE JAVA LANGUAGE JAVA EXTERNAL NAME " +
+                    "'" + TestStoredProcedureQueryFixes.class.getName() + ".sum'", false);
+
+            StoredProcedureQuery spq = em.createStoredProcedureQuery("XSUM");
+            spq.registerStoredProcedureParameter(1, Integer.class, ParameterMode.IN);
+            spq.registerStoredProcedureParameter(2, Integer.class, ParameterMode.OUT);
+            spq.registerStoredProcedureParameter(3, Integer.class, ParameterMode.IN);
+            spq.setParameter(1, 3);
+            spq.setParameter(3, 4);
+            spq.execute();
+
+            assertEquals(7, spq.getOutputParameterValue(2));
+        } finally {
+            em.close();
+        }
+    }
+
+    // Derby stored procedure: s = a + b
+    public static void sum(int a, int[] s, int b) {
+        s[0] = a + b;
+    }
+
     // Derby stored procedure: returns empty result set
     public static void emptyResultSet(java.sql.ResultSet[] rs) throws Exception {
         java.sql.Connection c = java.sql.DriverManager.getConnection("jdbc:default:connection");