diff --git a/.travis.yml b/.travis.yml
index d63fe13dfa..f6f43acb66 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,7 @@ dist: trusty
 sudo: false
 language: rust
 rust:
-- 1.12.0
+- 1.20.0
 - stable
 - beta
 - nightly
diff --git a/README.md b/README.md
index c61ba4a644..8828183014 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,7 @@ by [RE2](https://github.com/google/re2).
 [![Build status](https://ci.appveyor.com/api/projects/status/github/rust-lang/regex?svg=true)](https://ci.appveyor.com/project/rust-lang-libs/regex)
 [![Coverage Status](https://coveralls.io/repos/github/rust-lang/regex/badge.svg?branch=master)](https://coveralls.io/github/rust-lang/regex?branch=master)
 [![](http://meritbadge.herokuapp.com/regex)](https://crates.io/crates/regex)
+[![Rust](https://img.shields.io/badge/rust-1.20%2B-blue.svg?maxAge=3600)](https://github.com/rust-lang/regex)
 
 ### Documentation
 
@@ -210,7 +211,22 @@ recommended for general use.
 
 [Documentation `regex-syntax`.](https://docs.rs/regex-syntax)
 
-# License
+
+### Minimum Rust version policy
+
+This crate's minimum supported `rustc` version is `1.20.0`.
+
+The current **tentative** policy is that the minimum Rust version required to
+use this crate can be increased in minor version updates. For example, if
+regex 1.0.0 requires Rust 1.20.0, then regex 1.0.z for all values of `z` will
+also require Rust 1.20.0 or newer. However, regex 1.y for `y > 0` may require
+a newer minimum version of Rust.
+
+In general, this crate will be conservative with respect to the minimum
+supported version of Rust.
+
+
+### License
 
 This project is licensed under either of
 
diff --git a/ci/script.sh b/ci/script.sh
index baaca969e6..64fafc0d37 100755
--- a/ci/script.sh
+++ b/ci/script.sh
@@ -8,15 +8,6 @@ set -ex
 cargo build --verbose
 cargo doc --verbose
 
-# If we're testing on an older version of Rust, then only check that we
-# can build the crate. This is because the dev dependencies might be updated
-# more frequently, and therefore might require a newer version of Rust.
-#
-# This isn't ideal. It's a compromise.
-if [ "$TRAVIS_RUST_VERSION" = "1.12.0" ]; then
-  exit
-fi
-
 # Run tests. If we have nightly, then enable our nightly features.
 if [ "$TRAVIS_RUST_VERSION" = "nightly" ]; then
   cargo test --verbose --features unstable
diff --git a/src/vector/avx2.rs b/src/vector/avx2.rs
index 28f89d6a76..db0532c3fe 100644
--- a/src/vector/avx2.rs
+++ b/src/vector/avx2.rs
@@ -54,21 +54,13 @@ impl AVX2VectorBuilder {
     }
 }
 
-// We define our union with a macro so that our code continues to compile on
-// Rust 1.12.
-macro_rules! defunion {
-    () => {
-        #[derive(Clone, Copy)]
-        #[allow(non_camel_case_types)]
-        pub union u8x32 {
-            vector: __m256i,
-            bytes: [u8; 32],
-        }
-    }
+#[derive(Clone, Copy)]
+#[allow(non_camel_case_types)]
+pub union u8x32 {
+    vector: __m256i,
+    bytes: [u8; 32],
 }
 
-defunion!();
-
 impl u8x32 {
     #[inline]
     unsafe fn splat(n: u8) -> u8x32 {
diff --git a/src/vector/ssse3.rs b/src/vector/ssse3.rs
index 4107381d15..0485657f01 100644
--- a/src/vector/ssse3.rs
+++ b/src/vector/ssse3.rs
@@ -66,30 +66,22 @@ impl SSSE3VectorBuilder {
     }
 }
 
-// We define our union with a macro so that our code continues to compile on
-// Rust 1.12.
-macro_rules! defunion {
-    () => {
-        /// A u8x16 is a 128-bit vector with 16 single-byte lanes.
-        ///
-        /// It provides a safe API that uses only SSE2 or SSSE3 instructions.
-        /// The only way for callers to construct a value of this type is
-        /// through the SSSE3VectorBuilder type, and the only way to get a
-        /// SSSE3VectorBuilder is if the `ssse3` target feature is enabled.
-        ///
-        /// Note that generally speaking, all uses of this type should get
-        /// inlined, otherwise you probably have a performance bug.
-        #[derive(Clone, Copy)]
-        #[allow(non_camel_case_types)]
-        pub union u8x16 {
-            vector: __m128i,
-            bytes: [u8; 16],
-        }
-    }
+/// A u8x16 is a 128-bit vector with 16 single-byte lanes.
+///
+/// It provides a safe API that uses only SSE2 or SSSE3 instructions.
+/// The only way for callers to construct a value of this type is
+/// through the SSSE3VectorBuilder type, and the only way to get a
+/// SSSE3VectorBuilder is if the `ssse3` target feature is enabled.
+///
+/// Note that generally speaking, all uses of this type should get
+/// inlined, otherwise you probably have a performance bug.
+#[derive(Clone, Copy)]
+#[allow(non_camel_case_types)]
+pub union u8x16 {
+    vector: __m128i,
+    bytes: [u8; 16],
 }
 
-defunion!();
-
 impl u8x16 {
     #[inline]
     unsafe fn splat(n: u8) -> u8x16 {