diff --git a/src/interpreter/mod.rs b/src/interpreter/mod.rs
index 15fa4cdd3b842..6c0d58f1c47e7 100644
--- a/src/interpreter/mod.rs
+++ b/src/interpreter/mod.rs
@@ -1189,7 +1189,7 @@ impl<'a, 'b, 'mir, 'tcx> FnEvalContext<'a, 'b, 'mir, 'tcx> {
                 match *literal {
                     Value { ref value } => Ok(self.const_to_ptr(value)?),
                     Item { def_id, substs } => {
-                        if ty.is_fn() {
+                        if let ty::TyFnDef(..) = ty.sty {
                             Err(EvalError::Unimplemented("unimplemented: mentions of function items".to_string()))
                         } else {
                             let cid = ConstantId {
diff --git a/src/interpreter/stepper.rs b/src/interpreter/stepper.rs
index 587239fdf068d..db7b129eee601 100644
--- a/src/interpreter/stepper.rs
+++ b/src/interpreter/stepper.rs
@@ -8,7 +8,7 @@ use super::{
 };
 use error::EvalResult;
 use rustc::mir::repr as mir;
-use rustc::ty::subst;
+use rustc::ty::{subst, self};
 use rustc::hir::def_id::DefId;
 use rustc::mir::visit::{Visitor, LvalueContext};
 use syntax::codemap::Span;
@@ -151,7 +151,7 @@ impl<'a, 'b, 'mir, 'tcx> Visitor<'tcx> for ConstantExtractor<'a, 'b, 'mir, 'tcx>
             // already computed by rustc
             mir::Literal::Value { .. } => {}
             mir::Literal::Item { def_id, substs } => {
-                if constant.ty.is_fn() {
+                if let ty::TyFnDef(..) = constant.ty.sty {
                     // No need to do anything here, even if function pointers are implemented,
                     // because the type is the actual function, not the signature of the function.
                     // Thus we can simply create a zero sized allocation in `evaluate_operand`