diff --git a/.travis.yml b/.travis.yml
index beb65cc..69920fd 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,13 +17,14 @@ env:
     - LD_LIBRARY_PATH: /usr/local/lib
 script:
   # interleave building and testing in hope that it saves time
+  # also vary the local time zone to (hopefully) catch tz-dependent bugs
   # also avoid doc-testing multiple times---it takes a lot and rarely helps
   - cargo build -v
-  - cargo test -v
+  - TZ=ACST-9:30 cargo test -v
   - cargo build -v --features rustc-serialize
-  - cargo test -v --features rustc-serialize --lib
+  - TZ=EST4 cargo test -v --features rustc-serialize --lib
   - cargo build -v --features 'serde bincode'
-  - cargo test -v --features 'serde bincode' --lib
+  - TZ=UTC0 cargo test -v --features 'serde bincode' --lib
 notifications:
   email: false
   irc:
diff --git a/Makefile b/Makefile
index e39ffcf..40c5fc1 100644
--- a/Makefile
+++ b/Makefile
@@ -45,7 +45,9 @@ README.md: src/lib.rs
 
 .PHONY: test
 test:
-	cargo test --features 'serde rustc-serialize bincode'
+	TZ=UTC0 cargo test --features 'serde rustc-serialize bincode' --lib
+	TZ=ACST-9:30 cargo test --features 'serde rustc-serialize bincode' --lib
+	TZ=EST4 cargo test --features 'serde rustc-serialize bincode'
 
 .PHONY: doc
 doc: authors readme