diff --git a/src/librustc_passes/rvalue_promotion.rs b/src/librustc_passes/rvalue_promotion.rs
index 356ad9ec11bb7..76cbc67096988 100644
--- a/src/librustc_passes/rvalue_promotion.rs
+++ b/src/librustc_passes/rvalue_promotion.rs
@@ -373,10 +373,14 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>, e: &hir::Expr, node
             }
         }
         hir::ExprMethodCall(..) => {
-            let def_id = v.tables.type_dependent_defs()[e.hir_id].def_id();
-            match v.tcx.associated_item(def_id).container {
-                ty::ImplContainer(_) => v.handle_const_fn_call(def_id, node_ty),
-                ty::TraitContainer(_) => v.promotable = false
+            if let Some(def) = v.tables.type_dependent_defs().get(e.hir_id) {
+                let def_id = def.def_id();
+                match v.tcx.associated_item(def_id).container {
+                    ty::ImplContainer(_) => v.handle_const_fn_call(def_id, node_ty),
+                    ty::TraitContainer(_) => v.promotable = false
+                }
+            } else {
+                v.tcx.sess.delay_span_bug(e.span, "no type-dependent def for method call");
             }
         }
         hir::ExprStruct(..) => {
diff --git a/src/test/ui/type-dependent-def-issue-49241.rs b/src/test/ui/type-dependent-def-issue-49241.rs
new file mode 100644
index 0000000000000..64264999fd2f1
--- /dev/null
+++ b/src/test/ui/type-dependent-def-issue-49241.rs
@@ -0,0 +1,15 @@
+// Copyright 2018 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.
+
+fn main() {
+    let v = vec![0];
+    const l: usize = v.count(); //~ ERROR can't capture dynamic environment in a fn item
+    let s: [u32; l] = v.into_iter().collect(); //~ ERROR constant evaluation error
+}
diff --git a/src/test/ui/type-dependent-def-issue-49241.stderr b/src/test/ui/type-dependent-def-issue-49241.stderr
new file mode 100644
index 0000000000000..f00edccae5d50
--- /dev/null
+++ b/src/test/ui/type-dependent-def-issue-49241.stderr
@@ -0,0 +1,18 @@
+error[E0434]: can't capture dynamic environment in a fn item
+  --> $DIR/type-dependent-def-issue-49241.rs:13:22
+   |
+LL |     const l: usize = v.count(); //~ ERROR can't capture dynamic environment in a fn item
+   |                      ^
+   |
+   = help: use the `|| { ... }` closure form instead
+
+error[E0080]: constant evaluation error
+  --> $DIR/type-dependent-def-issue-49241.rs:14:18
+   |
+LL |     let s: [u32; l] = v.into_iter().collect(); //~ ERROR constant evaluation error
+   |                  ^ encountered constants with type errors, stopping evaluation
+
+error: aborting due to 2 previous errors
+
+Some errors occurred: E0080, E0434.
+For more information about an error, try `rustc --explain E0080`.