diff --git a/libgomp/ChangeLog b/libgomp/ChangeLog
index 420f354c51a79980f69370224640bed82df6b42b..b9f4a8a883edf7fdb8239690a4846f9a15215b0f 100644
--- a/libgomp/ChangeLog
+++ b/libgomp/ChangeLog
@@ -1,3 +1,13 @@
+2010-03-22  Jakub Jelinek  <jakub@redhat.com>
+
+	PR libgomp/42942
+	* env.c (parse_unsigned_long): Add ALLOW_ZERO argument.
+	(initialize_env): Adjust callers.
+	(omp_set_max_active_levels): Set gomp_max_active_levels_var even
+	when the argument is 0.
+
+	* testsuite/libgomp.c/pr42942.c: New test.
+
 2010-03-08  Tobias Grosser  <grosser@fim.uni-passau.de>
 
 	PR middle-end/42644
diff --git a/libgomp/env.c b/libgomp/env.c
index c870433f332318884e88530f15d3a9234531e889..3eb51e8a7d6d8287bd002bf52f05063cd46e4075 100644
--- a/libgomp/env.c
+++ b/libgomp/env.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
+/* Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010
+   Free Software Foundation, Inc.
    Contributed by Richard Henderson <rth@redhat.com>.
 
    This file is part of the GNU OpenMP Library (libgomp).
@@ -145,7 +146,7 @@ parse_schedule (void)
    present and it was successfully parsed.  */
 
 static bool
-parse_unsigned_long (const char *name, unsigned long *pvalue)
+parse_unsigned_long (const char *name, unsigned long *pvalue, bool allow_zero)
 {
   char *env, *end;
   unsigned long value;
@@ -161,7 +162,7 @@ parse_unsigned_long (const char *name, unsigned long *pvalue)
 
   errno = 0;
   value = strtoul (env, &end, 10);
-  if (errno || (long) value <= 0)
+  if (errno || (long) value <= 0 - allow_zero)
     goto invalid;
 
   while (isspace ((unsigned char) *end))
@@ -481,8 +482,9 @@ initialize_env (void)
   parse_schedule ();
   parse_boolean ("OMP_DYNAMIC", &gomp_global_icv.dyn_var);
   parse_boolean ("OMP_NESTED", &gomp_global_icv.nest_var);
-  parse_unsigned_long ("OMP_MAX_ACTIVE_LEVELS", &gomp_max_active_levels_var);
-  parse_unsigned_long ("OMP_THREAD_LIMIT", &gomp_thread_limit_var);
+  parse_unsigned_long ("OMP_MAX_ACTIVE_LEVELS", &gomp_max_active_levels_var,
+		       true);
+  parse_unsigned_long ("OMP_THREAD_LIMIT", &gomp_thread_limit_var, false);
   if (gomp_thread_limit_var != ULONG_MAX)
     gomp_remaining_threads_count = gomp_thread_limit_var - 1;
 #ifndef HAVE_SYNC_BUILTINS
@@ -490,7 +492,8 @@ initialize_env (void)
 #endif
   gomp_init_num_threads ();
   gomp_available_cpus = gomp_global_icv.nthreads_var;
-  if (!parse_unsigned_long ("OMP_NUM_THREADS", &gomp_global_icv.nthreads_var))
+  if (!parse_unsigned_long ("OMP_NUM_THREADS", &gomp_global_icv.nthreads_var,
+			    false))
     gomp_global_icv.nthreads_var = gomp_available_cpus;
   if (parse_affinity ())
     gomp_init_affinity ();
@@ -632,7 +635,7 @@ omp_get_thread_limit (void)
 void
 omp_set_max_active_levels (int max_levels)
 {
-  if (max_levels > 0)
+  if (max_levels >= 0)
     gomp_max_active_levels_var = max_levels;
 }
 
diff --git a/libgomp/testsuite/libgomp.c/pr42942.c b/libgomp/testsuite/libgomp.c/pr42942.c
new file mode 100644
index 0000000000000000000000000000000000000000..5d57852450ad329fc2e38b6ce9c3778129f24858
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/pr42942.c
@@ -0,0 +1,61 @@
+/* PR libgomp/42942 */
+/* { dg-do run } */
+
+#include <omp.h>
+#include <stdlib.h>
+
+int
+main (void)
+{
+  int e = 0;
+  omp_set_dynamic (0);
+  omp_set_nested (1);
+  omp_set_max_active_levels (1);
+  if (omp_get_max_active_levels () != 1)
+    abort ();
+#pragma omp parallel num_threads(2) reduction(|:e)
+  if (!omp_in_parallel ()
+      || omp_get_num_threads () != 2)
+    e = 1;
+  else
+#pragma omp parallel num_threads(2) reduction(|:e)
+    if (!omp_in_parallel ()
+	|| omp_get_num_threads () != 1)
+      e = 1;
+  if (e)
+    abort ();
+  omp_set_max_active_levels (0);
+  if (omp_get_max_active_levels () != 0)
+    abort ();
+#pragma omp parallel num_threads(2) reduction(|:e)
+  if (omp_in_parallel ()
+      || omp_get_num_threads () != 1)
+    e = 1;
+  else
+#pragma omp parallel num_threads(2) reduction(|:e)
+    if (omp_in_parallel ()
+	|| omp_get_num_threads () != 1)
+      e = 1;
+  if (e)
+    abort ();
+  omp_set_max_active_levels (2);
+  if (omp_get_max_active_levels () != 2)
+    abort ();
+#pragma omp parallel num_threads(2) reduction(|:e)
+  if (!omp_in_parallel ()
+      || omp_get_num_threads () != 2)
+    e = 1;
+  else
+#pragma omp parallel num_threads(2) reduction(|:e)
+    if (!omp_in_parallel ()
+	|| omp_get_num_threads () != 2)
+      e = 1;
+    else
+#pragma omp parallel num_threads(2) reduction(|:e)
+      if (!omp_in_parallel ()
+	  || omp_get_num_threads () != 1)
+	e = 1;
+  if (e)
+    abort ();
+  return 0;
+}