diff -r 0173e45cf7ab java.source/src/org/netbeans/modules/java/source/parsing/JavacParser.java
--- a/java.source/src/org/netbeans/modules/java/source/parsing/JavacParser.java	Wed Jan 23 19:15:45 2013 +0100
+++ b/java.source/src/org/netbeans/modules/java/source/parsing/JavacParser.java	Wed Jan 23 22:24:25 2013 +0100
@@ -822,6 +822,7 @@
 
     private static @NonNull com.sun.tools.javac.code.Source validateSourceLevel(@NullAllowed String sourceLevel, ClasspathInfo cpInfo) {
         ClassPath bootClassPath = cpInfo.getClassPath(PathKind.BOOT);
+        ClassPath cmpClassPath = cpInfo.getClassPath(PathKind.COMPILE);
         ClassPath srcClassPath = cpInfo.getClassPath(PathKind.SOURCE);
         com.sun.tools.javac.code.Source[] sources = com.sun.tools.javac.code.Source.values();
         Level warnLevel;
@@ -837,22 +838,32 @@
                 if (source.compareTo(com.sun.tools.javac.code.Source.JDK1_4) >= 0) {
                     if (bootClassPath != null && bootClassPath.findResource("java/lang/AssertionError.class") == null) { //NOI18N
                         if (srcClassPath != null && srcClassPath.findResource("java/lang/AssertionError.java") == null) {
-                            LOGGER.log(warnLevel,
+                            if (bootClassPath.getRoots().length != 0 ||
+                                cmpClassPath == null ||
+                                cmpClassPath.findResource("java/lang/AssertionError.class") == null
+                            ) {
+                                LOGGER.log(warnLevel,
                                        "Even though the source level of {0} is set to: {1}, java.lang.AssertionError cannot be found on the bootclasspath: {2}\n" +
                                        "Changing source level to 1.3",
                                        new Object[]{cpInfo.getClassPath(PathKind.SOURCE), sourceLevel, bootClassPath}); //NOI18N
-                            return com.sun.tools.javac.code.Source.JDK1_3;
+                                return com.sun.tools.javac.code.Source.JDK1_3;
+                            }
                         }
                     }
                 }
                 if (source.compareTo(com.sun.tools.javac.code.Source.JDK1_5) >= 0) {
                     if (bootClassPath != null && bootClassPath.findResource("java/lang/StringBuilder.class") == null) { //NOI18N
                         if (srcClassPath != null && srcClassPath.findResource("java/lang/StringBuilder.java")==null) {
-                            LOGGER.log(warnLevel,
+                            if (bootClassPath.getRoots().length != 0 ||
+                                cmpClassPath == null ||
+                                cmpClassPath.findResource("java/lang/StringBuilder.class") == null
+                            ) {
+                                LOGGER.log(warnLevel,
                                        "Even though the source level of {0} is set to: {1}, java.lang.StringBuilder cannot be found on the bootclasspath: {2}\n" +
                                        "Changing source level to 1.4",
                                        new Object[]{cpInfo.getClassPath(PathKind.SOURCE), sourceLevel, bootClassPath}); //NOI18N
-                            return com.sun.tools.javac.code.Source.JDK1_4;
+                                return com.sun.tools.javac.code.Source.JDK1_4;
+                            }
                         }
                     }
                 }