diff --git a/src/librustc/session/config.rs b/src/librustc/session/config.rs
index eb629dc44c156..3744746f1531a 100644
--- a/src/librustc/session/config.rs
+++ b/src/librustc/session/config.rs
@@ -1233,7 +1233,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "prints the llvm optimization passes being run"),
     ast_json: bool = (false, parse_bool, [UNTRACKED],
         "print the AST as JSON and halt"),
-    threads: Option<usize> = (None, parse_opt_uint, [UNTRACKED],
+    threads: Option<usize> = (Some(1), parse_opt_uint, [UNTRACKED],
         "use a thread pool with N threads"),
     ast_json_noexpand: bool = (false, parse_bool, [UNTRACKED],
         "print the pre-expansion AST as JSON and halt"),
diff --git a/src/librustc_data_structures/sync.rs b/src/librustc_data_structures/sync.rs
index 73247c1469efd..7bc6f7b360b8e 100644
--- a/src/librustc_data_structures/sync.rs
+++ b/src/librustc_data_structures/sync.rs
@@ -311,47 +311,58 @@ cfg_if! {
 
         use std;
         use std::thread;
-        pub use rayon::{join, scope};
+        
+        pub use self::serial_join as join;
+        pub use self::serial_scope as scope;
 
-        /// Runs a list of blocks in parallel. The first block is executed immediately on
-        /// the current thread. Use that for the longest running block.
         #[macro_export]
         macro_rules! parallel {
-            (impl $fblock:tt [$($c:tt,)*] [$block:tt $(, $rest:tt)*]) => {
-                parallel!(impl $fblock [$block, $($c,)*] [$($rest),*])
-            };
-            (impl $fblock:tt [$($blocks:tt,)*] []) => {
-                ::rustc_data_structures::sync::scope(|s| {
-                    $(
-                        s.spawn(|_| $blocks);
-                    )*
-                    $fblock;
-                })
-            };
-            ($fblock:tt, $($blocks:tt),*) => {
-                // Reverse the order of the later blocks since Rayon executes them in reverse order
-                // when using a single thread. This ensures the execution order matches that
-                // of a single threaded rustc
-                parallel!(impl $fblock [] [$($blocks),*]);
-            };
+            ($($blocks:tt),*) => {
+                // We catch panics here ensuring that all the blocks execute.
+                // This makes behavior consistent with the parallel compiler.
+                let mut panic = None;
+                $(
+                    if let Err(p) = ::std::panic::catch_unwind(
+                        ::std::panic::AssertUnwindSafe(|| $blocks)
+                    ) {
+                        if panic.is_none() {
+                            panic = Some(p);
+                        }
+                    }
+                )*
+                if let Some(panic) = panic {
+                    ::std::panic::resume_unwind(panic);
+                }
+            }
         }
 
         pub use rayon_core::WorkerLocal;
+        use std::panic::{resume_unwind, catch_unwind, AssertUnwindSafe};
 
-        pub use rayon::iter::ParallelIterator;
-        use rayon::iter::IntoParallelIterator;
+        pub use std::iter::Iterator as ParallelIterator;
 
-        pub fn par_iter<T: IntoParallelIterator>(t: T) -> T::Iter {
-            t.into_par_iter()
+        pub fn par_iter<T: IntoIterator>(t: T) -> T::IntoIter {
+            t.into_iter()
         }
 
-        pub fn par_for_each_in<T: IntoParallelIterator>(
+        pub fn par_for_each_in<T: IntoIterator>(
             t: T,
-            for_each: impl Fn(
-                <<T as IntoParallelIterator>::Iter as ParallelIterator>::Item
-            ) + Sync + Send
+            for_each:
+                impl Fn(<<T as IntoIterator>::IntoIter as Iterator>::Item) + Sync + Send
         ) {
-            t.into_par_iter().for_each(for_each)
+            // We catch panics here ensuring that all the loop iterations execute.
+            // This makes behavior consistent with the parallel compiler.
+            let mut panic = None;
+            t.into_iter().for_each(|i| {
+                if let Err(p) = catch_unwind(AssertUnwindSafe(|| for_each(i))) {
+                    if panic.is_none() {
+                        panic = Some(p);
+                    }
+                }
+            });
+            if let Some(panic) = panic {
+                resume_unwind(panic);
+            }
         }
 
         pub type MetadataRef = OwningRef<Box<dyn Erased + Send + Sync>, [u8]>;