diff --git a/.appveyor.yml b/.appveyor.yml
index a46214a3c45c..e97380cb932f 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -3,9 +3,7 @@ environment:
         PROJECT_NAME: miri
     matrix:
         - TARGET: x86_64-pc-windows-msvc
-          MSYS2_BITS: 64
         - TARGET: i686-pc-windows-msvc
-          MSYS2_BITS: 32
 
 # branches to build
 branches:
@@ -13,18 +11,23 @@ branches:
   only:
     - master
 
+cache:
+    - '%USERPROFILE%\.cargo'
+    - '%USERPROFILE%\.rustup'
+
 install:
-    # Install Rust.
-    - set PATH=C:\Program Files\Git\mingw64\bin;C:\msys64\mingw%MSYS2_BITS%\bin;%PATH%
-    - set /p RUST_TOOLCHAIN=<rust-version
+    # Install Rust
     - curl -sSf -o rustup-init.exe https://win.rustup.rs/
-    - rustup-init.exe -y --default-host %TARGET% --default-toolchain %RUST_TOOLCHAIN%
+    - rustup-init.exe -y --default-host %TARGET% --default-toolchain stable
     - set PATH=%USERPROFILE%\.cargo\bin;%PATH%
+    # Install "master" toolchain
+    - cargo install rustup-toolchain-install-master
+    - set /p RUSTC_HASH=<rust-version
+    - rustup-toolchain-install-master -f -n master %RUSTC_HASH% -c cargo -c rust-src
+    - rustup default master
     - rustc --version
 
-build: false
-
-test_script:
+build_script:
     - set RUST_TEST_NOCAPTURE=1
     - set RUST_BACKTRACE=1
     # Build and install miri
@@ -33,11 +36,18 @@ test_script:
     # Get ourselves a MIR-full libstd, and use it henceforth
     - cargo miri setup
     - set MIRI_SYSROOT=%USERPROFILE%\AppData\Local\miri\miri\cache\HOST
+
+test_script:
     # Test miri
     - cargo test --release --all-features
     # Test cargo integration
     - cd test-cargo-miri
-    - python3 run-test.py
+    - '"C:\msys64\mingw64\bin\python3.exe" run-test.py'
+
+after_test:
+    # Don't cache "master" toolchain, it's a waste
+    - rustup default stable
+    - rustup toolchain uninstall master
 
 notifications:
     - provider: Email
diff --git a/.travis.yml b/.travis.yml
index ee58f73c3643..883404fb4a08 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,7 +4,8 @@ cache:
   # we cannot reuse anyway when the nightly changes (and it grows quite large
   # over time).
   directories:
-    - /home/travis/.cargo
+    - $HOME/.cargo
+    - $HOME/.rustup
 
 os:
 - linux
@@ -17,18 +18,27 @@ before_script:
 # Compute the rust version we use. We do not use "language: rust" to have more control here.
 - |
   if [[ "$TRAVIS_EVENT_TYPE" == cron ]]; then
-    RUST_TOOLCHAIN=nightly
+    RUSTC_HASH=$(git ls-remote https://github.com/rust-lang/rust.git master | awk '{print $1}')
   else
-    RUST_TOOLCHAIN=$(cat rust-version)
+    RUSTC_HASH=$(cat rust-version)
   fi
-# install Rust
-- curl https://build.travis-ci.org/files/rustup-init.sh -sSf | sh -s -- -y --default-toolchain "$RUST_TOOLCHAIN"
+# Install Rust ("stable" toolchain for better caching, it is just used to build rustup-toolchain-install-master)
+- curl https://build.travis-ci.org/files/rustup-init.sh -sSf | sh -s -- -y --default-toolchain stable
 - export PATH=$HOME/.cargo/bin:$PATH
+# Install "master" toolchain
+- cargo install rustup-toolchain-install-master || echo "rustup-toolchain-install-master already installed"
+- travis_retry rustup-toolchain-install-master -f -n master $RUSTC_HASH -c cargo -c rust-src
+- rustup default master
 - rustc --version
 
 script:
 - ./travis.sh
 
+before_cache:
+# Don't cache "master" toolchain, it's a waste
+- rustup default stable
+- rustup toolchain uninstall master
+
 notifications:
   email:
     on_success: never
diff --git a/README.md b/README.md
index cf7bc9e32d0b..54d8411b2fe7 100644
--- a/README.md
+++ b/README.md
@@ -120,13 +120,18 @@ other projects:
 
 ```sh
 rustup component remove miri # avoid having Miri installed twice
-cargo +nightly install --path "$DIR" --force # or the nightly in `rust-version`
+cargo +nightly install --path "$DIR" --force
 cargo +nightly miri setup
 ```
 
 (We are giving `+nightly` explicitly here all the time because it is important
 that all of these commands get executed with the same toolchain.)
 
+In case this fails, your nightly might be incompatible with Miri master.  The
+`rust-version` file contains the commit hash of rustc that Miri is currently
+tested against; you can use that to find a nightly that works or you might have
+to wait for the next nightly to get released.
+
 If you want to use a different libstd (not the one that comes with the
 nightly), you can do that by running
 
diff --git a/rust-version b/rust-version
index b62147121802..a2b3daad97ec 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-nightly-2019-04-03
+f717b58dd70829f105960a071c7992b440720482