diff --git a/Cargo.lock b/Cargo.lock
index 6b1758610a670..32e4d9208a687 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2053,8 +2053,7 @@ dependencies = [
 [[package]]
 name = "chrono-tz"
 version = "0.10.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a6139a8597ed92cf816dfb33f5dd6cf0bb93a6adc938f11039f371bc5bcd26c3"
+source = "git+https://github.com/MaterializeInc/chrono-tz.git?rev=5999cdd1b971694f834ec3467d11ef9147fc297c#5999cdd1b971694f834ec3467d11ef9147fc297c"
 dependencies = [
  "chrono",
  "chrono-tz-build",
@@ -2066,8 +2065,7 @@ dependencies = [
 [[package]]
 name = "chrono-tz-build"
 version = "0.5.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c7d8d1efd5109b9c1cd3b7966bd071cdfb53bb6eb0b22a473a68c2f70a11a1eb"
+source = "git+https://github.com/MaterializeInc/chrono-tz.git?rev=5999cdd1b971694f834ec3467d11ef9147fc297c#5999cdd1b971694f834ec3467d11ef9147fc297c"
 dependencies = [
  "parse-zoneinfo",
  "phf_codegen 0.12.1",
@@ -10030,8 +10028,7 @@ dependencies = [
 [[package]]
 name = "parse-zoneinfo"
 version = "0.4.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e3c406c9e2aa74554e662d2c2ee11cd3e73756988800be7e6f5eddb16fed4699"
+source = "git+https://github.com/MaterializeInc/chrono-tz.git?rev=5999cdd1b971694f834ec3467d11ef9147fc297c#5999cdd1b971694f834ec3467d11ef9147fc297c"
 
 [[package]]
 name = "paste"
diff --git a/Cargo.toml b/Cargo.toml
index 41bdd81398750..97f71cb67ac9d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -650,6 +650,12 @@ postgres-types = { git = "https://github.com/MaterializeInc/rust-postgres" }
 postgres-openssl = { git = "https://github.com/MaterializeInc/rust-postgres" }
 postgres_array = { git = "https://github.com/MaterializeInc/rust-postgres-array" }
 
+# Upstream chrono-tz is unmaintained and stops at tzdata 2025b. The fork's
+# `mz_changes` branch carries current IANA data only, no code changes. To bump
+# tzdata, update the fork, then follow the bump ceremony documented in
+# src/environmentd/tests/testdata/timezones/regenerate.sh.
+chrono-tz = { git = "https://github.com/MaterializeInc/chrono-tz.git", rev = "5999cdd1b971694f834ec3467d11ef9147fc297c" }
+
 # Waiting on https://github.com/MaterializeInc/serde-value/pull/35.
 serde-value = { git = "https://github.com/MaterializeInc/serde-value.git" }
 
diff --git a/src/environmentd/tests/testdata/timezones/names-2026-12-15.csv b/src/environmentd/tests/testdata/timezones/names-2026-12-15.csv
index f74cbc1d46d22..a70d1bcb76355 100644
--- a/src/environmentd/tests/testdata/timezones/names-2026-12-15.csv
+++ b/src/environmentd/tests/testdata/timezones/names-2026-12-15.csv
@@ -12,14 +12,14 @@ Africa/Blantyre,CAT,02:00:00,f
 Africa/Brazzaville,WAT,01:00:00,f
 Africa/Bujumbura,CAT,02:00:00,f
 Africa/Cairo,EET,02:00:00,f
-Africa/Casablanca,+01,01:00:00,f
+Africa/Casablanca,+00,00:00:00,f
 Africa/Ceuta,CET,01:00:00,f
 Africa/Conakry,GMT,00:00:00,f
 Africa/Dakar,GMT,00:00:00,f
 Africa/Dar_es_Salaam,EAT,03:00:00,f
 Africa/Djibouti,EAT,03:00:00,f
 Africa/Douala,WAT,01:00:00,f
-Africa/El_Aaiun,+01,01:00:00,f
+Africa/El_Aaiun,+00,00:00:00,f
 Africa/Freetown,GMT,00:00:00,f
 Africa/Gaborone,CAT,02:00:00,f
 Africa/Harare,CAT,02:00:00,f
@@ -107,7 +107,7 @@ America/Dawson_Creek,MST,-07:00:00,f
 America/Denver,MST,-07:00:00,f
 America/Detroit,EST,-05:00:00,f
 America/Dominica,AST,-04:00:00,f
-America/Edmonton,MST,-07:00:00,f
+America/Edmonton,CST,-06:00:00,f
 America/Eirunepe,-05,-05:00:00,f
 America/El_Salvador,CST,-06:00:00,f
 America/Ensenada,PST,-08:00:00,f
@@ -215,12 +215,12 @@ America/Thunder_Bay,EST,-05:00:00,f
 America/Tijuana,PST,-08:00:00,f
 America/Toronto,EST,-05:00:00,f
 America/Tortola,AST,-04:00:00,f
-America/Vancouver,PST,-08:00:00,f
+America/Vancouver,MST,-07:00:00,f
 America/Virgin,AST,-04:00:00,f
 America/Whitehorse,MST,-07:00:00,f
 America/Winnipeg,CST,-06:00:00,f
 America/Yakutat,AKST,-09:00:00,f
-America/Yellowknife,MST,-07:00:00,f
+America/Yellowknife,CST,-06:00:00,f
 Antarctica/Casey,+08,08:00:00,f
 Antarctica/Davis,+07,07:00:00,f
 Antarctica/DumontDUrville,+10,10:00:00,f
@@ -375,9 +375,9 @@ Brazil/West,-04,-04:00:00,f
 Canada/Atlantic,AST,-04:00:00,f
 Canada/Central,CST,-06:00:00,f
 Canada/Eastern,EST,-05:00:00,f
-Canada/Mountain,MST,-07:00:00,f
+Canada/Mountain,CST,-06:00:00,f
 Canada/Newfoundland,NST,-03:30:00,f
-Canada/Pacific,PST,-08:00:00,f
+Canada/Pacific,MST,-07:00:00,f
 Canada/Saskatchewan,CST,-06:00:00,f
 Canada/Yukon,MST,-07:00:00,f
 CET,CET,01:00:00,f
diff --git a/src/environmentd/tests/testdata/timezones/regenerate.sh b/src/environmentd/tests/testdata/timezones/regenerate.sh
index a1cae366cff29..6d0013dccbb9d 100755
--- a/src/environmentd/tests/testdata/timezones/regenerate.sh
+++ b/src/environmentd/tests/testdata/timezones/regenerate.sh
@@ -29,7 +29,7 @@ set -euo pipefail
 
 cd "$(dirname "$0")"
 
-EXPECTED_TZDATA=2025b
+EXPECTED_TZDATA=2026c
 IMAGE=mz-timezone-snapshot
 
 DATES=("$@")
diff --git a/test/sqllogictest/timezone.slt b/test/sqllogictest/timezone.slt
index 53026cadaa1cf..1c53b705565ad 100644
--- a/test/sqllogictest/timezone.slt
+++ b/test/sqllogictest/timezone.slt
@@ -358,6 +358,44 @@ SELECT timezone_offset('Asia/Almaty', '2026-07-15 00:00:00 UTC'), timezone_offse
 (+05,05:00:00,00:00:00)
 (EEST,02:00:00,01:00:00)
 
+# Zones whose rules changed in tzdata 2025c through 2026c: Morocco moved to
+# permanent +00 on 2026-09-20, Alberta and British Columbia abolished DST on
+# their 2026 fall-back dates and keep the summer offset, and Moldova follows
+# EU transition instants. Both Canadian zones now render a neighbouring
+# region's standard-time abbreviation for their permanent offset.
+
+statement ok
+SET unsafe_new_transaction_wall_time = '2026-12-15 00:00:00 UTC';
+
+query TTTT
+SELECT * FROM pg_catalog.pg_timezone_names
+WHERE name IN ('Africa/Casablanca', 'America/Edmonton', 'America/Vancouver', 'Europe/Chisinau')
+ORDER BY name
+----
+Africa/Casablanca
++00
+00:00:00
+false
+America/Edmonton
+CST
+-06:00:00
+false
+America/Vancouver
+MST
+-07:00:00
+false
+Europe/Chisinau
+EET
+02:00:00
+false
+
+query TTT
+SELECT timezone_offset('Africa/Casablanca', '2026-09-21 00:00:00 UTC'), timezone_offset('America/Edmonton', '2026-11-15 00:00:00 UTC'), timezone_offset('America/Vancouver', '2026-11-15 00:00:00 UTC')
+----
+(+00,00:00:00,00:00:00)
+(CST,-06:00:00,00:00:00)
+(MST,-07:00:00,00:00:00)
+
 # These pin historical rules: a timestamp from before a zone's rule change
 # must resolve under the rules in force at that instant, not current rules.
 
@@ -385,3 +423,22 @@ query T
 SELECT timezone_offset('Asia/Choibalsan', '1995-06-15 00:00:00 UTC')
 ----
 (+09,08:00:00,01:00:00)
+
+# Moldova has switched at the EU instant, 01:00 UTC, since 2022. Older data
+# had it one hour earlier, so for one hour around each transition the two
+# disagree. This asserts the current belief about the past. If a data update
+# breaks it, IANA rewrote history.
+
+query T
+SELECT timezone_offset('Europe/Chisinau', '2023-03-26 00:30:00 UTC')
+----
+(EET,02:00:00,00:00:00)
+
+# Baja California observed DST in 1953 and 1961 through 1975, following
+# California, where earlier data had none. This asserts the current belief
+# about the past. If a data update breaks it, IANA rewrote history.
+
+query T
+SELECT timezone_offset('America/Tijuana', '1970-07-15 12:00:00 UTC')
+----
+(PDT,-08:00:00,01:00:00)