diff --git a/.travis.yml b/.travis.yml
index 48ab1f20c..b3b750207 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -34,7 +34,16 @@ before_install:
           fi;
           sudo apt-get install -y libobjc-4.8-dev libblocksruntime-dev;
         else
-          sudo apt-get install -y libkqueue-dev libpthread-workqueue-dev;
+          curl -s -o - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -;
+          sudo apt-add-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-9 main" && sudo apt-get update -qq;
+          sudo apt-get install -y clang-9 libkqueue-dev libpthread-workqueue-dev;
+          sudo update-alternatives   --install /usr/bin/clang   clang   /usr/bin/clang-9   10 \
+                                     --slave   /usr/bin/clang++ clang++ /usr/bin/clang++-9;
+          export PATH=$(echo "$PATH" | sed -e 's/:\/usr\/local\/clang-7.0.0\/bin//');
+          if [ "$RUNTIME_VERSION" = "gnustep-2.0" ];
+          then
+             sudo update-alternatives --install "/usr/bin/ld" "ld" "/usr/bin/ld.gold" 10;
+          fi;
         fi;
     # libdispatch requires a fairly recent version of cmake
     - >
@@ -59,5 +68,5 @@ before_script: >
     export GNUSTEP_MAKEFILES=$HOME/staging/share/GNUstep/Makefiles;
     . $HOME/staging/share/GNUstep/Makefiles/GNUstep.sh;
 script: >
-    ./configure $BASE_ABI;
+    ./configure $BASE_ABI || (cat config.log && false);
     make && make install && make check || (cat Tests/tests.log && false);
diff --git a/Tests/base/NSArray/blocks.m b/Tests/base/NSArray/blocks.m
index 9112e39d5..ec8a20a9b 100644
--- a/Tests/base/NSArray/blocks.m
+++ b/Tests/base/NSArray/blocks.m
@@ -4,10 +4,12 @@
 #import <Foundation/NSIndexSet.h>
 #import <Foundation/NSString.h>
 #import <Foundation/NSEnumerator.h>
+#import <Foundation/NSLock.h>
 #import <Foundation/NSValue.h>
 
 static NSUInteger fooCount = 0;
 static NSUInteger lastIndex = NSNotFound;
+static BOOL reverse = NO;
 int main()
 {
   START_SET("NSArray Blocks")
@@ -16,10 +18,20 @@ int main()
 # endif
 # if __has_feature(blocks)
   NSAutoreleasePool   *arp = [NSAutoreleasePool new];
-
+  NSLock *lock = [[[NSLock alloc] init] autorelease];
   NSArray *array = [NSArray arrayWithObjects: @"foo", @"bar", @"foo", nil];
-  void(^enumBlock)(id,NSUInteger,BOOL*) =  ^(id obj, NSUInteger index, BOOL *stop){
-    if ([obj isEqual: @"foo"]){ fooCount++;} lastIndex = index;};
+  void(^enumBlock)(id,NSUInteger,BOOL*) =  ^(id obj, NSUInteger index, BOOL *stop) {
+   [lock lock];
+   if ([obj isEqual: @"foo"]) {
+      fooCount++;
+    }
+    if (lastIndex == NSNotFound) {
+      lastIndex = index;
+    } else {
+      lastIndex = reverse ? MIN(lastIndex, index) : MAX(lastIndex, index);
+    }
+    [lock unlock];
+  };
   [array enumerateObjectsUsingBlock: enumBlock];
   PASS((2 == fooCount) && (lastIndex == 2),
        "Can forward enumerate array using a block");
@@ -31,9 +43,11 @@ int main()
        "Can forward enumerate array concurrently using a block");
   fooCount = 0;
   lastIndex = NSNotFound;
+  reverse = YES;
   [array enumerateObjectsWithOptions: NSEnumerationReverse
                           usingBlock: enumBlock];
   PASS((0 == lastIndex), "Can enumerate array in reverse using a block");
+  reverse = NO;
   fooCount = 0;
   lastIndex = NSNotFound;
   enumBlock = ^(id obj, NSUInteger index, BOOL *stop){if ([obj isEqual: @"foo"]){