diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs
index f04119241310..bd8b3e678d85 100644
--- a/src/librustc/ty/context.rs
+++ b/src/librustc/ty/context.rs
@@ -1942,8 +1942,12 @@ pub mod tls {
     /// This is a callback from libsyntax as it cannot access the implicit state
     /// in librustc otherwise
     fn span_debug(span: syntax_pos::Span, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        with(|tcx| {
-            write!(f, "{}", tcx.sess.source_map().span_to_string(span))
+        with_opt(|tcx| {
+            if let Some(tcx) = tcx {
+                write!(f, "{}", tcx.sess.source_map().span_to_string(span))
+            } else {
+                syntax_pos::default_span_debug(span, f)
+            }
         })
     }
 
diff --git a/src/libsyntax_pos/lib.rs b/src/libsyntax_pos/lib.rs
index 4d42b85ea754..4e3d1e89a721 100644
--- a/src/libsyntax_pos/lib.rs
+++ b/src/libsyntax_pos/lib.rs
@@ -611,7 +611,7 @@ impl serialize::UseSpecializedDecodable for Span {
     }
 }
 
-fn default_span_debug(span: Span, f: &mut fmt::Formatter) -> fmt::Result {
+pub fn default_span_debug(span: Span, f: &mut fmt::Formatter) -> fmt::Result {
     f.debug_struct("Span")
         .field("lo", &span.lo())
         .field("hi", &span.hi())