diff --git a/src/librustc/middle/infer/higher_ranked/mod.rs b/src/librustc/middle/infer/higher_ranked/mod.rs
index 5d3e2dc9c93e3149c175f5040dd09d8219fb2467..0df84323ae53f4d64aa07df1acce62989a1aa1df 100644
--- a/src/librustc/middle/infer/higher_ranked/mod.rs
+++ b/src/librustc/middle/infer/higher_ranked/mod.rs
@@ -468,7 +468,7 @@ pub fn skolemize_late_bound_regions<'a,'tcx,T>(infcx: &InferCtxt<'a,'tcx>,
      * when higher-ranked things are involved. See `doc.rs` for more details.
      */
 
-    let (result, map) = ty::replace_late_bound_regions(infcx.tcx, binder, |br, _| {
+    let (result, map) = ty::replace_late_bound_regions(infcx.tcx, binder, |br| {
         infcx.region_vars.new_skolemized(br, &snapshot.region_vars_snapshot)
     });
 
diff --git a/src/librustc/middle/infer/mod.rs b/src/librustc/middle/infer/mod.rs
index 57893ec97a2186fd673adc2e8526440005a41574..ab1c41f69683eb074ecb8dd5a9eaa857bdebd84a 100644
--- a/src/librustc/middle/infer/mod.rs
+++ b/src/librustc/middle/infer/mod.rs
@@ -1048,7 +1048,7 @@ pub fn replace_late_bound_regions_with_fresh_var<T>(
         ty::replace_late_bound_regions(
             self.tcx,
             value,
-            |br, _| self.next_region_var(LateBoundRegion(span, br, lbrct)))
+            |br| self.next_region_var(LateBoundRegion(span, br, lbrct)))
     }
 
     /// See `verify_generic_bound` method in `region_inference`
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index 33efc1fa10b6c4016524de4d3cafe301fb7963cb..64f0bcb1c88db280d4bc73b44f0fcc260bba4fa2 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -6686,7 +6686,7 @@ pub fn liberate_late_bound_regions<'tcx, T>(
 {
     replace_late_bound_regions(
         tcx, value,
-        |br, _| ty::ReFree(ty::FreeRegion{scope: scope, bound_region: br})).0
+        |br| ty::ReFree(ty::FreeRegion{scope: scope, bound_region: br})).0
 }
 
 pub fn count_late_bound_regions<'tcx, T>(
@@ -6695,7 +6695,7 @@ pub fn count_late_bound_regions<'tcx, T>(
     -> uint
     where T : TypeFoldable<'tcx> + Repr<'tcx>
 {
-    let (_, skol_map) = replace_late_bound_regions(tcx, value, |_, _| ty::ReStatic);
+    let (_, skol_map) = replace_late_bound_regions(tcx, value, |_| ty::ReStatic);
     skol_map.len()
 }
 
@@ -6726,7 +6726,7 @@ pub fn erase_late_bound_regions<'tcx, T>(
     -> T
     where T : TypeFoldable<'tcx> + Repr<'tcx>
 {
-    replace_late_bound_regions(tcx, value, |_, _| ty::ReStatic).0
+    replace_late_bound_regions(tcx, value, |_| ty::ReStatic).0
 }
 
 /// Rewrite any late-bound regions so that they are anonymous.  Region numbers are
@@ -6744,9 +6744,9 @@ pub fn anonymize_late_bound_regions<'tcx, T>(
     where T : TypeFoldable<'tcx> + Repr<'tcx>,
 {
     let mut counter = 0;
-    ty::Binder(replace_late_bound_regions(tcx, sig, |_, db| {
+    ty::Binder(replace_late_bound_regions(tcx, sig, |_| {
         counter += 1;
-        ReLateBound(db, BrAnon(counter))
+        ReLateBound(ty::DebruijnIndex::new(1), BrAnon(counter))
     }).0)
 }
 
@@ -6757,7 +6757,7 @@ pub fn replace_late_bound_regions<'tcx, T, F>(
     mut mapf: F)
     -> (T, FnvHashMap<ty::BoundRegion,ty::Region>)
     where T : TypeFoldable<'tcx> + Repr<'tcx>,
-          F : FnMut(BoundRegion, DebruijnIndex) -> ty::Region,
+          F : FnMut(BoundRegion) -> ty::Region,
 {
     debug!("replace_late_bound_regions({})", binder.repr(tcx));
 
@@ -6769,8 +6769,19 @@ pub fn replace_late_bound_regions<'tcx, T, F>(
         debug!("region={}", region.repr(tcx));
         match region {
             ty::ReLateBound(debruijn, br) if debruijn.depth == current_depth => {
-                * map.entry(br).get().unwrap_or_else(
-                      |vacant_entry| vacant_entry.insert(mapf(br, debruijn)))
+                let region =
+                    * map.entry(br).get().unwrap_or_else(
+                        |vacant_entry| vacant_entry.insert(mapf(br)));
+
+                if let ty::ReLateBound(debruijn1, br) = region {
+                    // If the callback returns a late-bound region,
+                    // that region should always use depth 1. Then we
+                    // adjust it to the correct depth.
+                    assert_eq!(debruijn1.depth, 1);
+                    ty::ReLateBound(debruijn, br)
+                } else {
+                    region
+                }
             }
             _ => {
                 region
diff --git a/src/librustc/middle/ty_fold.rs b/src/librustc/middle/ty_fold.rs
index dedd69deabb0b27a864fb6e9ff341e3325980e56..b81a4ed2f58ff79f76a0f197111056e75346a64d 100644
--- a/src/librustc/middle/ty_fold.rs
+++ b/src/librustc/middle/ty_fold.rs
@@ -862,7 +862,10 @@ fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 ///////////////////////////////////////////////////////////////////////////
 // Region eraser
 //
-// Replaces all free regions with 'static. Useful in trans.
+// Replaces all free regions with 'static. Useful in contexts, such as
+// method probing, where precise region relationships are not
+// important. Note that in trans you should use
+// `common::erase_regions` instead.
 
 pub struct RegionEraser<'a, 'tcx: 'a> {
     tcx: &'a ty::ctxt<'tcx>,
diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs
index b510fedc5f95245307efb57253c21a40d407909d..559ec533baa9eca1ed0a67d7bbca462541c5ad9f 100644
--- a/src/librustc/util/ppaux.rs
+++ b/src/librustc/util/ppaux.rs
@@ -1183,8 +1183,8 @@ fn user_string(&self, tcx: &ctxt<'tcx>) -> String {
         // the output. We'll probably want to tweak this over time to
         // decide just how much information to give.
         let mut names = Vec::new();
-        let (unbound_value, _) = ty::replace_late_bound_regions(tcx, self, |br, debruijn| {
-            ty::ReLateBound(debruijn, match br {
+        let (unbound_value, _) = ty::replace_late_bound_regions(tcx, self, |br| {
+            ty::ReLateBound(ty::DebruijnIndex::new(1), match br {
                 ty::BrNamed(_, name) => {
                     names.push(token::get_name(name));
                     br
diff --git a/src/librustc_trans/trans/base.rs b/src/librustc_trans/trans/base.rs
index 78fe7861854dd351cfc548da43c849c9b708c638..74071a1de4c3d080c797133c0db7a5d1577a1342 100644
--- a/src/librustc_trans/trans/base.rs
+++ b/src/librustc_trans/trans/base.rs
@@ -281,8 +281,15 @@ pub fn kind_for_unboxed_closure(ccx: &CrateContext, closure_id: ast::DefId)
 
 pub fn decl_rust_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
                               fn_ty: Ty<'tcx>, name: &str) -> ValueRef {
+    debug!("decl_rust_fn(fn_ty={}, name={:?})",
+           fn_ty.repr(ccx.tcx()),
+           name);
+
     let fn_ty = monomorphize::normalize_associated_type(ccx.tcx(), &fn_ty);
 
+    debug!("decl_rust_fn: fn_ty={} (after normalized associated types)",
+           fn_ty.repr(ccx.tcx()));
+
     let function_type; // placeholder so that the memory ownership works out ok
 
     let (sig, abi, env) = match fn_ty.sty {
@@ -305,10 +312,12 @@ pub fn decl_rust_fn<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
     let sig = ty::erase_late_bound_regions(ccx.tcx(), sig);
     let sig = ty::Binder(sig);
 
+    debug!("decl_rust_fn: sig={} (after erasing regions)",
+           sig.repr(ccx.tcx()));
+
     let llfty = type_of_rust_fn(ccx, env, &sig, abi);
 
-    debug!("decl_rust_fn(sig={}, type={})",
-           sig.repr(ccx.tcx()),
+    debug!("decl_rust_fn: llfty={}",
            ccx.tn().type_to_string(llfty));
 
     let llfn = decl_fn(ccx, name, llvm::CCallConv, llfty, sig.0.output /* (1) */);
diff --git a/src/librustc_trans/trans/callee.rs b/src/librustc_trans/trans/callee.rs
index 274c3e0a50ae3405ac1169c4b7b379e573949ae5..6196f9e5eab65eff401594f9cfad0699ecfd9378 100644
--- a/src/librustc_trans/trans/callee.rs
+++ b/src/librustc_trans/trans/callee.rs
@@ -265,7 +265,7 @@ pub fn trans_fn_pointer_shim<'a, 'tcx>(
     let _icx = push_ctxt("trans_fn_pointer_shim");
     let tcx = ccx.tcx();
 
-    let bare_fn_ty = normalize_ty(tcx, bare_fn_ty);
+    let bare_fn_ty = erase_regions(tcx, &bare_fn_ty);
     match ccx.fn_pointer_shims().borrow().get(&bare_fn_ty) {
         Some(&llval) => { return llval; }
         None => { }
diff --git a/src/librustc_trans/trans/closure.rs b/src/librustc_trans/trans/closure.rs
index 76f82c14e0a8a5b6f8dacd5daf5ffeed2c1873e6..8989dfd493236a80c186f4dcb5105b1d0819b7a8 100644
--- a/src/librustc_trans/trans/closure.rs
+++ b/src/librustc_trans/trans/closure.rs
@@ -466,7 +466,7 @@ pub fn get_or_create_declaration_if_unboxed_closure<'a, 'tcx>(ccx: &CrateContext
 
     // Normalize type so differences in regions and typedefs don't cause
     // duplicate declarations
-    let function_type = normalize_ty(ccx.tcx(), function_type);
+    let function_type = erase_regions(ccx.tcx(), &function_type);
     let params = match function_type.sty {
         ty::ty_unboxed_closure(_, _, ref substs) => substs.types.clone(),
         _ => unreachable!()
diff --git a/src/librustc_trans/trans/common.rs b/src/librustc_trans/trans/common.rs
index 1a74137c10df6c528858d2389dfedb52904116bc..ab5b563b99c7259ada392acf0ac6b1e427515d45 100644
--- a/src/librustc_trans/trans/common.rs
+++ b/src/librustc_trans/trans/common.rs
@@ -58,16 +58,21 @@
 
 pub use trans::context::CrateContext;
 
-/// Returns an equivalent type with all the typedefs and self regions removed.
-pub fn normalize_ty<'tcx>(cx: &ty::ctxt<'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
-    let u = TypeNormalizer(cx).fold_ty(ty);
-    debug!("normalize_ty({}) = {}",
-           ty.repr(cx), u.repr(cx));
-    return u;
+/// Returns an equivalent value with all free regions removed (note
+/// that late-bound regions remain, because they are important for
+/// subtyping, but they are anonymized and normalized as well). This
+/// is a stronger, caching version of `ty_fold::erase_regions`.
+pub fn erase_regions<'tcx,T>(cx: &ty::ctxt<'tcx>, value: &T) -> T
+    where T : TypeFoldable<'tcx> + Repr<'tcx>
+{
+    let value1 = value.fold_with(&mut RegionEraser(cx));
+    debug!("erase_regions({}) = {}",
+           value.repr(cx), value1.repr(cx));
+    return value1;
 
-    struct TypeNormalizer<'a, 'tcx: 'a>(&'a ty::ctxt<'tcx>);
+    struct RegionEraser<'a, 'tcx: 'a>(&'a ty::ctxt<'tcx>);
 
-    impl<'a, 'tcx> TypeFolder<'tcx> for TypeNormalizer<'a, 'tcx> {
+    impl<'a, 'tcx> TypeFolder<'tcx> for RegionEraser<'a, 'tcx> {
         fn tcx(&self) -> &ty::ctxt<'tcx> { self.0 }
 
         fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
@@ -84,7 +89,6 @@ fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
         fn fold_binder<T>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T>
             where T : TypeFoldable<'tcx> + Repr<'tcx>
         {
-            // FIXME(#20526) this should replace `enter_region_binder`/`exit_region_binder`.
             let u = ty::anonymize_late_bound_regions(self.tcx(), t);
             ty_fold::super_fold_binder(self, &u)
         }
@@ -989,7 +993,7 @@ pub fn fulfill_obligation<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>,
 let tcx = ccx.tcx();
 
 // Remove any references to regions; this helps improve caching.
-let trait_ref = ty_fold::erase_regions(tcx, trait_ref);
+let trait_ref = erase_regions(tcx, &trait_ref);
 
 // First check the cache.
 match ccx.trait_cache().borrow().get(&trait_ref) {
diff --git a/src/librustc_trans/trans/monomorphize.rs b/src/librustc_trans/trans/monomorphize.rs
index 435f94f35fa8aaab9c708bee94446fb08e18badf..93076260349abd5c81aee5d5801823a800ec4a2d 100644
--- a/src/librustc_trans/trans/monomorphize.rs
+++ b/src/librustc_trans/trans/monomorphize.rs
@@ -313,8 +313,10 @@ pub fn normalize_associated_type<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> T
 {
     debug!("normalize_associated_type(t={})", value.repr(tcx));
 
+    let value = erase_regions(tcx, value);
+
     if !value.has_projection_types() {
-        return value.clone();
+        return value;
     }
 
     // FIXME(#20304) -- cache
@@ -324,7 +326,7 @@ pub fn normalize_associated_type<'tcx,T>(tcx: &ty::ctxt<'tcx>, value: &T) -> T
     let mut selcx = traits::SelectionContext::new(&infcx, &typer);
     let cause = traits::ObligationCause::dummy();
     let traits::Normalized { value: result, obligations } =
-        traits::normalize(&mut selcx, cause, value);
+        traits::normalize(&mut selcx, cause, &value);
 
     debug!("normalize_associated_type: result={} obligations={}",
            result.repr(tcx),
diff --git a/src/librustc_trans/trans/type_of.rs b/src/librustc_trans/trans/type_of.rs
index c908441e3662b686f8f2891495afa79431e5adc6..034a1ee8be5925ef2903803cb4de9def9da020ec 100644
--- a/src/librustc_trans/trans/type_of.rs
+++ b/src/librustc_trans/trans/type_of.rs
@@ -285,7 +285,7 @@ fn type_of_unsize_info<'a, 'tcx>(cx: &CrateContext<'a, 'tcx>, t: Ty<'tcx>) -> Ty
     // Rust types are defined as the same LLVM types.  If we don't do
     // this then, e.g. `Option<{myfield: bool}>` would be a different
     // type than `Option<myrec>`.
-    let t_norm = normalize_ty(cx.tcx(), t);
+    let t_norm = erase_regions(cx.tcx(), &t);
 
     if t != t_norm {
         let llty = type_of(cx, t_norm);
diff --git a/src/test/run-pass/associated-types-region-erasure-issue-20582.rs b/src/test/run-pass/associated-types-region-erasure-issue-20582.rs
new file mode 100644
index 0000000000000000000000000000000000000000..03ab8f7e43136910ef3a75cb2672a875af6da184
--- /dev/null
+++ b/src/test/run-pass/associated-types-region-erasure-issue-20582.rs
@@ -0,0 +1,27 @@
+// 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.
+
+// Regression test for #20582. This test caused an ICE related to
+// inconsistent region erasure in trans.
+
+struct Foo<'a> {
+    buf: &'a[u8]
+}
+
+impl<'a> Iterator for Foo<'a> {
+    type Item = &'a[u8];
+
+    fn next(&mut self) -> Option<<Self as Iterator>::Item> {
+        Some(self.buf)
+    }
+}
+
+fn main() {
+}