diff --git a/icu4j/main/classes/core/src/com/ibm/icu/util/IslamicCalendar.java b/icu4j/main/classes/core/src/com/ibm/icu/util/IslamicCalendar.java
index 16d8caf9902..da254723474 100644
--- a/icu4j/main/classes/core/src/com/ibm/icu/util/IslamicCalendar.java
+++ b/icu4j/main/classes/core/src/com/ibm/icu/util/IslamicCalendar.java
@@ -1,6 +1,6 @@
 /*
  *******************************************************************************
- * Copyright (C) 1996-2008, International Business Machines Corporation and    *
+ * Copyright (C) 1996-2010, International Business Machines Corporation and    *
  * others. All Rights Reserved.                                                *
  *******************************************************************************
  */
@@ -438,7 +438,7 @@ public class IslamicCalendar extends Calendar {
         {
             // Make a guess at when the month started, using the average length
             long origin = HIJRA_MILLIS 
-                        + (long)Math.floor(month * CalendarAstronomer.SYNODIC_MONTH - 1) * ONE_DAY;
+                        + (long)Math.floor(month * CalendarAstronomer.SYNODIC_MONTH) * ONE_DAY;
 
             double age = moonAge(origin);
 
@@ -610,7 +610,7 @@ public class IslamicCalendar extends Calendar {
 
             monthStart = (long)Math.floor(months * CalendarAstronomer.SYNODIC_MONTH - 1);
 
-            if ( days - monthStart >= 28 && moonAge(internalGetTimeInMillis()) > 0) {
+            if ( days - monthStart >= 25 && moonAge(internalGetTimeInMillis()) > 0) {
                 // If we're near the end of the month, assume next month and search backwards
                 months++;
             }
diff --git a/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/IslamicTest.java b/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/IslamicTest.java
index 60f76066d6e..00e44c3d6dd 100644
--- a/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/IslamicTest.java
+++ b/icu4j/main/tests/core/src/com/ibm/icu/dev/test/calendar/IslamicTest.java
@@ -1,6 +1,6 @@
 /*
  *******************************************************************************
- * Copyright (C) 1996-2005, International Business Machines Corporation and    *
+ * Copyright (C) 1996-2010, International Business Machines Corporation and    *
  * others. All Rights Reserved.                                                *
  *******************************************************************************
  */
@@ -143,6 +143,16 @@ public class IslamicTest extends CalendarTest {
         IslamicCalendar islamic = newCivil();
         doLimitsTest(islamic, null, cal.getTime());
         doTheoreticalLimitsTest(islamic, true);
+
+
+        // number of days to test - Islamic calendar starts to exhibit 
+        // rounding errors after year AH3954 - about 2500 years out.
+
+        IslamicCalendar islamic2 = new IslamicCalendar();
+        islamic2.setCivil(false);
+        int testTime = getInclusion() <= 5 ? 20000 : 800000;
+        doLimitsTest(islamic2, null, cal.getTime(), testTime);
+        doTheoreticalLimitsTest(islamic2, true);
     }
 
     public void TestCoverage() {