diff --git a/src/librustc/hir/def_id.rs b/src/librustc/hir/def_id.rs
index f6fcff37ca53e..8858023ec1d7b 100644
--- a/src/librustc/hir/def_id.rs
+++ b/src/librustc/hir/def_id.rs
@@ -17,8 +17,8 @@ use std::u32;
 
 newtype_index!(CrateNum
     {
-        derive[Debug]
         ENCODABLE = custom
+        DEBUG_FORMAT = "crate{}",
 
         /// Item definitions in the currently-compiled crate would have the CrateNum
         /// LOCAL_CRATE in their DefId.
@@ -172,17 +172,19 @@ pub struct DefId {
 
 impl fmt::Debug for DefId {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "DefId {{ krate: {:?}, index: {:?}",
-               self.krate, self.index)?;
+        write!(f, "DefId({:?}/{}:{}",
+               self.krate.index(),
+               self.index.address_space().index(),
+               self.index.as_array_index())?;
 
         ty::tls::with_opt(|opt_tcx| {
             if let Some(tcx) = opt_tcx {
-                write!(f, " => {}", tcx.def_path_debug_str(*self))?;
+                write!(f, " ~ {}", tcx.def_path_debug_str(*self))?;
             }
             Ok(())
         })?;
 
-        write!(f, " }}")
+        write!(f, ")")
     }
 }
 
diff --git a/src/test/mir-opt/validate_1.rs b/src/test/mir-opt/validate_1.rs
index f4d1caa6a9553..b7360a0e08733 100644
--- a/src/test/mir-opt/validate_1.rs
+++ b/src/test/mir-opt/validate_1.rs
@@ -30,7 +30,7 @@ fn main() {
 // END RUST SOURCE
 // START rustc.{{impl}}-foo.EraseRegions.after.mir
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(0:5) => validate_1[317d]::{{impl}}[0]::foo[0] }, BrAnon(0)) Test, _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(0:5) => validate_1[317d]::{{impl}}[0]::foo[0] }, BrAnon(1)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId(0/0:5 ~ validate_1[317d]::{{impl}}[0]::foo[0]), BrAnon(0)) Test, _2: &ReFree(DefId(0/0:5 ~ validate_1[317d]::{{impl}}[0]::foo[0]), BrAnon(1)) mut i32]);
 //         ...
 //         return;
 //     }
@@ -62,7 +62,7 @@ fn main() {
 // fn main::{{closure}}(_1: &ReErased [closure@NodeId(50)], _2: &ReErased mut i32) -> i32 {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:11) => validate_1[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(50)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:11) => validate_1[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId(0/1:11 ~ validate_1[317d]::main[0]::{{closure}}[0]), BrEnv) [closure@NodeId(50)], _2: &ReFree(DefId(0/1:11 ~ validate_1[317d]::main[0]::{{closure}}[0]), BrAnon(0)) mut i32]);
 //         StorageLive(_3);
 //         Validate(Suspend(ReScope(Remainder(BlockRemainder { block: ItemLocalId(22), first_statement_index: 0 }))), [(*_2): i32]);
 //         _3 = &ReErased (*_2);
diff --git a/src/test/mir-opt/validate_4.rs b/src/test/mir-opt/validate_4.rs
index 80224ddc58668..39438af4b449a 100644
--- a/src/test/mir-opt/validate_4.rs
+++ b/src/test/mir-opt/validate_4.rs
@@ -51,8 +51,8 @@ fn main() {
 // fn write_42::{{closure}}(_1: &ReErased [closure@NodeId(22)], _2: *mut i32) -> () {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_4[317d]::write_42[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(22)], _2: *mut i32]);
-//         Validate(Release, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_4[317d]::write_42[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(22)], _2: *mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId(0/1:9 ~ validate_4[317d]::write_42[0]::{{closure}}[0]), BrEnv) [closure@NodeId(22)], _2: *mut i32]);
+//         Validate(Release, [_1: &ReFree(DefId(0/1:9 ~ validate_4[317d]::write_42[0]::{{closure}}[0]), BrEnv) [closure@NodeId(22)], _2: *mut i32]);
 //         (*_2) = const 23i32;
 //         return;
 //     }
@@ -62,8 +62,8 @@ fn main() {
 // fn test(_1: &ReErased mut i32) -> () {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(0:4) => validate_4[317d]::test[0] }, BrAnon(0)) mut i32]);
-//         Validate(Release, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(0:4) => validate_4[317d]::test[0] }, BrAnon(0)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId(0/0:4 ~ validate_4[317d]::test[0]), BrAnon(0)) mut i32]);
+//         Validate(Release, [_1: &ReFree(DefId(0/0:4 ~ validate_4[317d]::test[0]), BrAnon(0)) mut i32]);
 //         ...
 //         _2 = const write_42(_3) -> bb1;
 //     }
@@ -78,8 +78,8 @@ fn main() {
 // fn main::{{closure}}(_1: &ReErased [closure@NodeId(60)], _2: &ReErased mut i32) -> bool {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
-//         Validate(Release, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:10) => validate_4[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId(0/1:10 ~ validate_4[317d]::main[0]::{{closure}}[0]), BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId(0/1:10 ~ validate_4[317d]::main[0]::{{closure}}[0]), BrAnon(0)) mut i32]);
+//         Validate(Release, [_1: &ReFree(DefId(0/1:10 ~ validate_4[317d]::main[0]::{{closure}}[0]), BrEnv) [closure@NodeId(60)], _2: &ReFree(DefId(0/1:10 ~ validate_4[317d]::main[0]::{{closure}}[0]), BrAnon(0)) mut i32]);
 //         StorageLive(_3);
 //         ...
 //         _0 = const write_42(_3) -> bb1;
diff --git a/src/test/mir-opt/validate_5.rs b/src/test/mir-opt/validate_5.rs
index a945b7dbc5fa8..043338c808983 100644
--- a/src/test/mir-opt/validate_5.rs
+++ b/src/test/mir-opt/validate_5.rs
@@ -37,7 +37,7 @@ fn main() {
 // fn test(_1: &ReErased mut i32) -> () {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(0:4) => validate_5[317d]::test[0] }, BrAnon(0)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId(0/0:4 ~ validate_5[317d]::test[0]), BrAnon(0)) mut i32]);
 //         ...
 //         Validate(Release, [_2: bool, _3: *mut i32]);
 //         _2 = const write_42(_3) -> bb1;
@@ -49,7 +49,7 @@ fn main() {
 // fn main::{{closure}}(_1: &ReErased [closure@NodeId(46)], _2: &ReErased mut i32) -> bool {
 //     ...
 //     bb0: {
-//         Validate(Acquire, [_1: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_5[317d]::main[0]::{{closure}}[0] }, BrEnv) [closure@NodeId(46)], _2: &ReFree(DefId { krate: CrateNum(0), index: DefIndex(1:9) => validate_5[317d]::main[0]::{{closure}}[0] }, BrAnon(0)) mut i32]);
+//         Validate(Acquire, [_1: &ReFree(DefId(0/1:9 ~ validate_5[317d]::main[0]::{{closure}}[0]), BrEnv) [closure@NodeId(46)], _2: &ReFree(DefId(0/1:9 ~ validate_5[317d]::main[0]::{{closure}}[0]), BrAnon(0)) mut i32]);
 //         StorageLive(_3);
 //         StorageLive(_4);
 //         Validate(Suspend(ReScope(Node(ItemLocalId(9)))), [(*_2): i32]);