diff --git a/compiler/rustc_span/src/analyze_source_file.rs b/compiler/rustc_span/src/analyze_source_file.rs
index ba7e0cec5bd..28ce883daee 100644
--- a/compiler/rustc_span/src/analyze_source_file.rs
+++ b/compiler/rustc_span/src/analyze_source_file.rs
@@ -8,7 +8,7 @@
 ///
 /// This function will use an SSE2 enhanced implementation if hardware support
 /// is detected at runtime.
-pub fn analyze_source_file(src: &str) -> (Vec<RelativeBytePos>, Vec<MultiByteChar>) {
+pub(crate) fn analyze_source_file(src: &str) -> (Vec<RelativeBytePos>, Vec<MultiByteChar>) {
     let mut lines = vec![RelativeBytePos::from_u32(0)];
     let mut multi_byte_chars = vec![];
 
diff --git a/compiler/rustc_span/src/lib.rs b/compiler/rustc_span/src/lib.rs
index 7b020f11cdd..45dca3af6c0 100644
--- a/compiler/rustc_span/src/lib.rs
+++ b/compiler/rustc_span/src/lib.rs
@@ -30,6 +30,7 @@
 #![feature(round_char_boundary)]
 #![feature(rustc_attrs)]
 #![feature(rustdoc_internals)]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 // The code produced by the `Encodable`/`Decodable` derive macros refer to
diff --git a/compiler/rustc_span/src/span_encoding.rs b/compiler/rustc_span/src/span_encoding.rs
index 8988becb171..3047abfbb5c 100644
--- a/compiler/rustc_span/src/span_encoding.rs
+++ b/compiler/rustc_span/src/span_encoding.rs
@@ -424,7 +424,7 @@ pub fn parent(self) -> Option<LocalDefId> {
 }
 
 #[derive(Default)]
-pub struct SpanInterner {
+pub(crate) struct SpanInterner {
     spans: FxIndexSet<SpanData>,
 }