diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index b84046d105051..7a9422ef53d58 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -15,6 +15,7 @@ use codemap::{ExpnInfo, MacroBang, MacroAttribute, dummy_spanned, respan};
 use config::{is_test_or_bench, StripUnconfigured};
 use errors::{Applicability, FatalError};
 use ext::base::*;
+use ext::build::AstBuilder;
 use ext::derive::{add_derived_markers, collect_derives};
 use ext::hygiene::{self, Mark, SyntaxContext};
 use ext::placeholders::{placeholder, PlaceholderExpander};
@@ -474,6 +475,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 cx: self.cx,
                 invocations: Vec::new(),
                 monotonic: self.monotonic,
+                tests_nameable: true,
             };
             (fragment.fold_with(&mut collector), collector.invocations)
         };
@@ -1049,6 +1051,11 @@ struct InvocationCollector<'a, 'b: 'a> {
     cfg: StripUnconfigured<'a>,
     invocations: Vec<Invocation>,
     monotonic: bool,
+
+    /// Test functions need to be nameable. Tests inside functions or in other
+    /// unnameable locations need to be ignored. `tests_nameable` tracks whether
+    /// any test functions found in the current context would be nameable.
+    tests_nameable: bool,
 }
 
 impl<'a, 'b> InvocationCollector<'a, 'b> {
@@ -1066,6 +1073,20 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         placeholder(fragment_kind, NodeId::placeholder_from_mark(mark))
     }
 
+    /// Folds the item allowing tests to be expanded because they are still nameable.
+    /// This should probably only be called with module items
+    fn fold_nameable(&mut self, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
+        fold::noop_fold_item(item, self)
+    }
+
+    /// Folds the item but doesn't allow tests to occur within it
+    fn fold_unnameable(&mut self, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
+        let was_nameable = mem::replace(&mut self.tests_nameable, false);
+        let items = fold::noop_fold_item(item, self);
+        self.tests_nameable = was_nameable;
+        items
+    }
+
     fn collect_bang(&mut self, mac: ast::Mac, span: Span, kind: AstFragmentKind) -> AstFragment {
         self.collect(kind, InvocationKind::Bang { mac: mac, ident: None, span: span })
     }
@@ -1306,7 +1327,7 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
             }
             ast::ItemKind::Mod(ast::Mod { inner, .. }) => {
                 if item.ident == keywords::Invalid.ident() {
-                    return noop_fold_item(item, self);
+                    return self.fold_nameable(item);
                 }
 
                 let orig_directory_ownership = self.cx.current_expansion.directory_ownership;
@@ -1346,22 +1367,58 @@ impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
 
                 let orig_module =
                     mem::replace(&mut self.cx.current_expansion.module, Rc::new(module));
-                let result = noop_fold_item(item, self);
+                let result = self.fold_nameable(item);
                 self.cx.current_expansion.module = orig_module;
                 self.cx.current_expansion.directory_ownership = orig_directory_ownership;
                 result
             }
             // Ensure that test functions are accessible from the test harness.
+            // #[test] fn foo() {}
+            // becomes:
+            // #[test] pub fn foo_gensym(){}
+            // #[allow(unused)]
+            // use foo_gensym as foo;
             ast::ItemKind::Fn(..) if self.cx.ecfg.should_test => {
-                if item.attrs.iter().any(|attr| is_test_or_bench(attr)) {
+                if self.tests_nameable && item.attrs.iter().any(|attr| is_test_or_bench(attr)) {
+                    let orig_ident = item.ident;
+                    let orig_vis   = item.vis.clone();
+
+                    // Publicize the item under gensymed name to avoid pollution
                     item = item.map(|mut item| {
                         item.vis = respan(item.vis.span, ast::VisibilityKind::Public);
+                        item.ident = item.ident.gensym();
                         item
                     });
+
+                    // Use the gensymed name under the item's original visibility
+                    let mut use_item = self.cx.item_use_simple_(
+                        item.ident.span,
+                        orig_vis,
+                        Some(orig_ident),
+                        self.cx.path(item.ident.span,
+                            vec![keywords::SelfValue.ident(), item.ident]));
+
+                    // #[allow(unused)] because the test function probably isn't being referenced
+                    use_item = use_item.map(|mut ui| {
+                        ui.attrs.push(
+                            self.cx.attribute(DUMMY_SP, attr::mk_list_item(DUMMY_SP,
+                                Ident::from_str("allow"), vec![
+                                    attr::mk_nested_word_item(Ident::from_str("unused"))
+                                ]
+                            ))
+                        );
+
+                        ui
+                    });
+
+                    SmallVector::many(
+                        self.fold_unnameable(item).into_iter()
+                            .chain(self.fold_unnameable(use_item)))
+                } else {
+                    self.fold_unnameable(item)
                 }
-                noop_fold_item(item, self)
             }
-            _ => noop_fold_item(item, self),
+            _ => self.fold_unnameable(item),
         }
     }
 
diff --git a/src/test/run-pass/issue-52557.rs b/src/test/run-pass/issue-52557.rs
new file mode 100644
index 0000000000000..2b8dfe162cc3d
--- /dev/null
+++ b/src/test/run-pass/issue-52557.rs
@@ -0,0 +1,38 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// This test checks for namespace pollution by private tests.
+// Tests used to marked as public causing name conflicts with normal
+// functions only in test builds.
+
+// compile-flags: --test
+
+mod a {
+    pub fn foo() -> bool {
+        true
+    }
+}
+
+mod b {
+    #[test]
+    fn foo() {
+        local_name(); // ensure the local name still works
+    }
+
+    #[test]
+    fn local_name() {}
+}
+
+use a::*;
+use b::*;
+
+pub fn conflict() {
+    let _: bool = foo();
+}