diff --git a/miri b/miri
index 1f46f04c13e..6de2391137a 100755
--- a/miri
+++ b/miri
@@ -45,7 +45,7 @@ fi
 # We set the rpath so that Miri finds the private rustc libraries it needs.
 # We enable debug-assertions to get tracing.
 # We enable line-only debuginfo for backtraces.
-export RUSTFLAGS="-C link-args=-Wl,-rpath,$LIBDIR -C debug-assertions -C debuginfo=1"
+export RUSTFLAGS="-C link-args=-Wl,-rpath,$LIBDIR -C debug-assertions -C debuginfo=1 $RUSTC_EXTRA_FLAGS"
 
 ## Helper functions
 
diff --git a/travis.sh b/travis.sh
index c06dbaee363..6f14be44ef0 100755
--- a/travis.sh
+++ b/travis.sh
@@ -8,6 +8,7 @@ else
   FOREIGN_TARGET=i686-unknown-linux-gnu
 fi
 export CARGO_EXTRA_FLAGS="--all-features"
+export RUSTC_EXTRA_FLAGS="-D warnings"
 
 # Prepare
 echo "Build and install miri"