diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index 692d230446cda..8a061e3a528e7 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -243,6 +243,7 @@ pub struct Cache {
 
     stack: Vec<String>,
     parent_stack: Vec<DefId>,
+    parent_is_trait_impl: bool,
     search_index: Vec<IndexItem>,
     privmod: bool,
     remove_priv: bool,
@@ -487,6 +488,7 @@ pub fn run(mut krate: clean::Crate,
         stack: Vec::new(),
         parent_stack: Vec::new(),
         search_index: Vec::new(),
+        parent_is_trait_impl: false,
         extern_locations: HashMap::new(),
         primitive_locations: HashMap::new(),
         remove_priv: cx.passes.contains("strip-private"),
@@ -995,6 +997,11 @@ impl DocFolder for Cache {
         // Index this method for searching later on
         if let Some(ref s) = item.name {
             let (parent, is_method) = match item.inner {
+                clean::AssociatedConstItem(..) |
+                clean::TypedefItem(_, true) if self.parent_is_trait_impl => {
+                    // skip associated items in trait impls
+                    ((None, None), false)
+                }
                 clean::AssociatedTypeItem(..) |
                 clean::AssociatedConstItem(..) |
                 clean::TyMethodItem(..) |
@@ -1026,10 +1033,6 @@ impl DocFolder for Cache {
                         ((Some(*last), path), true)
                     }
                 }
-                clean::TypedefItem(_, true) => {
-                    // skip associated types in impls
-                    ((None, None), false)
-                }
                 _ => ((None, Some(&*self.stack)), false)
             };
             let hidden_field = match item.inner {
@@ -1115,12 +1118,15 @@ impl DocFolder for Cache {
         }
 
         // Maintain the parent stack
+        let orig_parent_is_trait_impl = self.parent_is_trait_impl;
         let parent_pushed = match item.inner {
             clean::TraitItem(..) | clean::EnumItem(..) | clean::StructItem(..) => {
                 self.parent_stack.push(item.def_id);
+                self.parent_is_trait_impl = false;
                 true
             }
             clean::ImplItem(ref i) => {
+                self.parent_is_trait_impl = i.trait_.is_some();
                 match i.for_ {
                     clean::ResolvedPath{ did, .. } => {
                         self.parent_stack.push(did);
@@ -1201,6 +1207,7 @@ impl DocFolder for Cache {
         if pushed { self.stack.pop().unwrap(); }
         if parent_pushed { self.parent_stack.pop().unwrap(); }
         self.privmod = orig_privmod;
+        self.parent_is_trait_impl = orig_parent_is_trait_impl;
         return ret;
     }
 }
diff --git a/src/test/rustdoc/issue-31808.rs b/src/test/rustdoc/issue-31808.rs
new file mode 100644
index 0000000000000..46be8229d7c65
--- /dev/null
+++ b/src/test/rustdoc/issue-31808.rs
@@ -0,0 +1,23 @@
+// Copyright 2016 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.
+
+#![feature(associated_consts, associated_types)]
+
+// Test that associated item impls on primitive types don't crash rustdoc
+
+pub trait Foo {
+    const BAR: usize;
+    type BAZ;
+}
+
+impl Foo for () {
+    const BAR: usize = 0;
+    type BAZ = usize;
+}