diff --git a/src/lib.rs b/src/lib.rs
index 2f632f6..784e456 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -220,10 +220,20 @@
 /// This type is semver exempt and not exposed by default.
 #[cfg(procmacro2_semver_exempt)]
 #[derive(Clone, PartialEq, Eq)]
-pub struct SourceFile(imp::SourceFile);
+pub struct SourceFile {
+    inner: imp::SourceFile,
+    _marker: marker::PhantomData<Rc<()>>,
+}
 
 #[cfg(procmacro2_semver_exempt)]
 impl SourceFile {
+    fn _new(inner: imp::SourceFile) -> Self {
+        SourceFile {
+            inner: inner,
+            _marker: marker::PhantomData,
+        }
+    }
+
     /// Get the path to this source file.
     ///
     /// ### Note
@@ -238,27 +248,27 @@
     ///
     /// [`is_real`]: #method.is_real
     pub fn path(&self) -> &FileName {
-        self.0.path()
+        self.inner.path()
     }
 
     /// Returns `true` if this source file is a real source file, and not
     /// generated by an external macro's expansion.
     pub fn is_real(&self) -> bool {
-        self.0.is_real()
+        self.inner.is_real()
     }
 }
 
 #[cfg(procmacro2_semver_exempt)]
 impl AsRef<FileName> for SourceFile {
     fn as_ref(&self) -> &FileName {
-        self.0.path()
+        self.inner.path()
     }
 }
 
 #[cfg(procmacro2_semver_exempt)]
 impl fmt::Debug for SourceFile {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        self.0.fmt(f)
+        self.inner.fmt(f)
     }
 }
 
@@ -344,7 +354,7 @@
     /// This method is semver exempt and not exposed by default.
     #[cfg(procmacro2_semver_exempt)]
     pub fn source_file(&self) -> SourceFile {
-        SourceFile(self.inner.source_file())
+        SourceFile::_new(self.inner.source_file())
     }
 
     /// Get the starting line/column in the source file for this span.