diff --git a/.appveyor.yml b/.appveyor.yml
index 7db60514ada7..5b77b1895a63 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -30,6 +30,7 @@ install:
 build_script:
     - set RUST_TEST_NOCAPTURE=1
     - set RUST_BACKTRACE=1
+    - set RUSTFLAGS="-C debug-assertions"
     # Build and install miri
     - cargo build --release --all-features --all-targets
     - cargo install --all-features --force --path .
diff --git a/.travis.yml b/.travis.yml
index 883404fb4a08..fd8c1260215d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -12,6 +12,12 @@ os:
 - osx
 dist: xenial
 
+env:
+  global:
+  - RUST_TEST_NOCAPTURE=1
+  - RUST_BACKTRACE=1
+  - RUSTFLAGS="-C debug-assertions"
+
 before_script:
 # Linux: install extra stuff for cross-compilation
 - if [[ "$TRAVIS_OS_NAME" == linux ]]; then sudo apt update && sudo apt install gcc-multilib; fi
@@ -48,7 +54,3 @@ notifications:
 branches:
   only:
   - master
-env:
-  global:
-  - RUST_TEST_NOCAPTURE=1
-  - RUST_BACKTRACE=1