diff --git a/.travis.yml b/.travis.yml
index 9d73d14..1aecb85 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,7 @@ branches:
 language: rust
 dist: xenial
 rust:
-    - nightly-2015-05-01 # see ct.sh for more versions
+    - nightly-2016-03-11 # see ct.sh for more versions
 env:
     - RUST_BACKTRACE=1
 before_script:
diff --git a/build.rs b/build.rs
index 178b0bb..c4c7f03 100644
--- a/build.rs
+++ b/build.rs
@@ -4,35 +4,45 @@ use std::env;
 use std::fs::File;
 use std::io::Write;
 use std::path::PathBuf;
-use std::ops::{Neg,Sub};
 
-/*
- * Let me explain this hack. For the sync shell script it's easiest if every 
- * line in mapping.rs looks exactly the same. This means that specifying an 
- * array literal is not possible. include!() can only expand to expressions, so 
- * just specifying the contents of an array is also not possible.
- *
- * This leaves us with trying to find an expression in which every line looks 
- * the same. This can be done using the `-` operator. This can be a unary 
- * operator (first thing on the first line), or a binary operator (later 
- * lines). That is exactly what's going on here, and Neg and Sub simply build a 
- * vector of the operangs.
- */
 struct Mapping(&'static str,&'static str);
 
-impl Neg for Mapping {
-	type Output = Vec<Mapping>;
-    fn neg(self) -> Vec<Mapping> {
-		vec![self.into()]
-	}
-}
+fn parse_mappings(mut mappings: &'static str) -> Vec<Mapping> {
+	// FIXME: The format used here used to be parsed directly by rustc, which
+	// is why it's kind of weird. It should be changed to a saner format.
 
-impl Sub<Mapping> for Vec<Mapping> {
-    type Output=Vec<Mapping>;
-    fn sub(mut self, rhs: Mapping) -> Vec<Mapping> {
-		self.push(rhs.into());
-		self
+	const P1: &'static str = r#"-Mapping(""#;
+	const P2: &'static str = r#"",""#; ;
+	const P3: &'static str = "\")\n";
+
+	trait TakePrefix: Sized {
+		fn take_prefix(&mut self, mid: usize) -> Self;
 	}
+
+	impl<'a> TakePrefix for &'a str {
+		fn take_prefix(&mut self, mid: usize) -> Self {
+			let prefix = &self[..mid];
+			*self = &self[mid..];
+			prefix
+		}
+	}
+
+	let mut result = Vec::with_capacity( mappings.len() / (P1.len()+40+P2.len()+40+P3.len()) );
+
+	while mappings.len() != 0 {
+		match (
+			mappings.take_prefix(P1.len()),
+			mappings.take_prefix(40),
+			mappings.take_prefix(P2.len()),
+			mappings.take_prefix(40),
+			mappings.take_prefix(P3.len()),
+		) {
+			(P1, hash1, P2, hash2, P3) => result.push(Mapping(hash1, hash2)),
+			_ => panic!("Invalid input in mappings"),
+		}
+	}
+
+	result
 }
 
 fn main() {
@@ -42,8 +52,8 @@ fn main() {
 		Ok(c) => c,
 		Err(env::VarError::NotUnicode(_)) => panic!("Invalid commit specified in CORE_IO_COMMIT"),
 		Err(env::VarError::NotPresent) => {
-			let mappings=include!("mapping.rs");
-			
+			let mappings=parse_mappings(include_str!("mapping.rs"));
+
 			let compiler=ver.commit_hash.expect("Couldn't determine compiler version");
 			mappings.iter().find(|&&Mapping(elem,_)|elem==compiler).expect("Unknown compiler version, upgrade core_io?").1.to_owned()
 		}
diff --git a/ct.sh b/ct.sh
index 3f0bad1..48a9703 100755
--- a/ct.sh
+++ b/ct.sh
@@ -1,21 +1,24 @@
 #!/bin/bash -e
+
+# Old versions should come first so we go from oldest Cargo.lock version to
+# newest when building.
 RUST_VERSIONS=$(awk '{print $1}' <<EOF
-    nightly-2019-04-27 # core_io release
-    nightly-2018-08-14 # edge case: old features disallowed
-    nightly-2018-08-06 # edge case: old features allowed
-    nightly-2018-03-07 # core_io release
-    nightly-2018-01-02 # edge case: memchr in core
-    nightly-2018-01-01 # edge case: no memchr in core
-    nightly-2017-06-16 # edge case: no collections crate
-    nightly-2017-06-15 # edge case: collections crate
-    nightly-2017-04-09 # core_io release
-    nightly-2017-03-04 # edge case: std_unicode crate
-    nightly-2017-03-03 # edge case: rustc_unicode crate
-    nightly-2017-01-18 # edge case: rustc_unicode crate
-    nightly-2016-12-05 # edge case: no unicode crate
-    nightly-2016-10-28 # core_io release
+    nightly-2016-03-11 # first supported version
     nightly-2016-07-07 # core_io release
-    nightly-2015-05-01 # some old version
+    nightly-2016-10-28 # core_io release
+    nightly-2016-12-05 # edge case: no unicode crate
+    nightly-2017-01-18 # edge case: rustc_unicode crate
+    nightly-2017-03-03 # edge case: rustc_unicode crate
+    nightly-2017-03-04 # edge case: std_unicode crate
+    nightly-2017-04-09 # core_io release
+    nightly-2017-06-15 # edge case: collections crate
+    nightly-2017-06-16 # edge case: no collections crate
+    nightly-2018-01-01 # edge case: no memchr in core
+    nightly-2018-01-02 # edge case: memchr in core
+    nightly-2018-03-07 # core_io release
+    nightly-2018-08-06 # edge case: old features allowed
+    nightly-2018-08-14 # edge case: old features disallowed
+    nightly-2019-04-27 # core_io release
 EOF
 )
 
diff --git a/src/lib.rs b/src/lib.rs
index 83ebe15..8a33f3a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -3,9 +3,9 @@
 //! the [std documentation](https://doc.rust-lang.org/nightly/std/io/index.html)
 //! for a full description of the functionality.
 #![allow(stable_features,unused_features)]
-#![feature(question_mark,const_fn,copy_from_slice,non_exhaustive,
-	bind_by_move_pattern_guards,try_from,str_internals,align_offset,doc_spotlight,
-	slice_internals)]
+#![feature(question_mark,const_fn,collections,alloc,unicode,copy_from_slice,
+	str_char,try_from,str_internals,align_offset,doc_spotlight,
+	slice_internals,non_exhaustive,bind_by_move_pattern_guards)]
 #![no_std]
 
 #[cfg_attr(feature="collections",macro_use)]