diff --git a/hledger-lib/package.yaml b/hledger-lib/package.yaml
index 4ae10bb49..a7e78c7ca 100644
--- a/hledger-lib/package.yaml
+++ b/hledger-lib/package.yaml
@@ -95,6 +95,8 @@ dependencies:
 - extra >=1.7.11
 - Glob >= 0.9
 
+language: GHC2021
+
 ghc-options:
 - -Wall
 - -Wno-incomplete-uni-patterns
diff --git a/hledger-ui/package.yaml b/hledger-ui/package.yaml
index b85a9be32..d8cb43592 100644
--- a/hledger-ui/package.yaml
+++ b/hledger-ui/package.yaml
@@ -58,6 +58,8 @@ flags:
 
 cpp-options: -DVERSION="1.50.99"
 
+language: GHC2021
+
 ghc-options:
 - -Wall
 - -Wno-incomplete-uni-patterns
diff --git a/hledger-web/package.yaml b/hledger-web/package.yaml
index d7ae3a598..b7d5c0321 100644
--- a/hledger-web/package.yaml
+++ b/hledger-web/package.yaml
@@ -68,6 +68,8 @@ flags:
 #    default: false
 #    manual:  true
 
+language: GHC2021
+
 ghc-options:
 - -Wall
 # not included in -Wall:
diff --git a/hledger/package.yaml b/hledger/package.yaml
index 00393793d..120d2bbe7 100644
--- a/hledger/package.yaml
+++ b/hledger/package.yaml
@@ -104,6 +104,8 @@ flags:
 #    default: false
 #    manual:  true
 
+language: GHC2021
+
 ghc-options:
 - -Wall
 - -Wno-incomplete-uni-patterns