Fastdebug builds crashes with assert "assert(workers() != 0,"no workers")" with ParallelGC and ParallelGCThreads=0:

jdk1.6.0_14//fastdebug/bin/java -XX:ParallelGCThreads=0 -XX:+UseParallelGC -version
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/BUILD_AREA/jdk6_14/hotspot/src/share/vm/gc_implementation/parallelScavenge/gcTaskManager.cpp:363), pid=10618, tid=4141939600
# Error: assert(workers() != 0,"no workers")
#
# JRE version: 6.0_14-b01
# Java VM: OpenJDK Server VM (14.0-b10-fastdebug mixed mode linux-x86 )
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#

Issue could be reproduced with latest JDK 6 and JDK 7 builds as well:
#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/HUDSON/workspace/jdk7u12-2-build-linux-i586-product/jdk7u12/hotspot/src/share/vm/gc_implementation/parallelScavenge/gcTaskManager.cpp:397), pid=11113, tid=4140850064
# assert(workers() != 0) failed: no workers
#
# JRE version: (7.0_12-b01)
# Java VM: Java HotSpot(TM) Server VM (24.0-b24-fastdebug mixed mode linux-x86 )
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#

--------------- T H R E A D ---------------

Current thread (0x082c9000): JavaThread "Unknown thread" [_thread_in_vm, id=11114, stack(0xf6cb5000,0xf6d06000)]

Stack: [0xf6cb5000,0xf6d06000], sp=0xf6d04d50, free space=319k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0xba814e] VMError::report_and_die()+0x1ae
V [libjvm.so+0x558d98] report_vm_error(char const*, int, char const*, char const*)+0x68
V [libjvm.so+0x65bfb9] GCTaskManager::initialize()+0x4c9
V [libjvm.so+0x9df773] ParallelScavengeHeap::initialize()+0x6d3
V [libjvm.so+0xb677c4] Universe::initialize_heap()+0xa4
V [libjvm.so+0xb679c0] universe_init()+0x90
V [libjvm.so+0x6cd64b] init_globals()+0x5b
V [libjvm.so+0xb40100] Threads::create_vm(JavaVMInitArgs*, bool*)+0x220
V [libjvm.so+0x734d4c] JNI_CreateJavaVM+0x8c
C [libjli.so+0x4688] JavaMain+0x98
C [libpthread.so.0+0x5832] abort@@GLIBC_2.0+0x5832