diff --git a/hledger-lib/hledger-lib.cabal b/hledger-lib/hledger-lib.cabal
index 7e7809d18..d128fd3e0 100644
--- a/hledger-lib/hledger-lib.cabal
+++ b/hledger-lib/hledger-lib.cabal
@@ -68,7 +68,7 @@ library
     , deepseq
     , directory
     , filepath
-    , megaparsec >=5
+    , megaparsec >=5 && < 5.1
     , mtl
     , mtl-compat
     , old-time
@@ -158,7 +158,7 @@ test-suite doctests
     , deepseq
     , directory
     , filepath
-    , megaparsec >=5
+    , megaparsec >=5 && < 5.1
     , mtl
     , mtl-compat
     , old-time
@@ -198,7 +198,7 @@ test-suite hunittests
     , deepseq
     , directory
     , filepath
-    , megaparsec >=5
+    , megaparsec >=5 && < 5.1
     , mtl
     , mtl-compat
     , old-time
diff --git a/hledger-lib/package.yaml b/hledger-lib/package.yaml
index 1417cdd43..714322e88 100644
--- a/hledger-lib/package.yaml
+++ b/hledger-lib/package.yaml
@@ -52,7 +52,7 @@ dependencies:
 - deepseq
 - directory
 - filepath
-- megaparsec >=5
+- megaparsec >=5 && < 5.1
 - mtl
 - mtl-compat
 - old-time
diff --git a/hledger-web/hledger-web.cabal b/hledger-web/hledger-web.cabal
index 4573e6a1a..9e51a0ab7 100644
--- a/hledger-web/hledger-web.cabal
+++ b/hledger-web/hledger-web.cabal
@@ -159,7 +159,7 @@ library
         , yesod-form
         , yesod-static
         , json
-        , megaparsec >=5
+        , megaparsec >=5 && < 5.1
         , mtl
     if (flag(dev)) || (flag(library-only))
         cpp-options: -DDEVELOPMENT
diff --git a/hledger-web/package.yaml b/hledger-web/package.yaml
index 120e0a23e..42ad82fe4 100644
--- a/hledger-web/package.yaml
+++ b/hledger-web/package.yaml
@@ -119,7 +119,7 @@ library:
   - Settings.Development
   - Settings.StaticFiles
   dependencies:
-  - megaparsec >=5
+  - megaparsec >=5 && < 5.1
   - mtl
   when:
   - condition: (flag(dev)) || (flag(library-only))
diff --git a/hledger/hledger.cabal b/hledger/hledger.cabal
index 782e8e1fd..51c51a35b 100644
--- a/hledger/hledger.cabal
+++ b/hledger/hledger.cabal
@@ -104,7 +104,7 @@ library
     , mtl
     , mtl-compat
     , old-time
-    , megaparsec >=5
+    , megaparsec >=5 && < 5.1
     , regex-tdfa
     , safe >=0.2
     , split >=0.1 && <0.3
diff --git a/hledger/package.yaml b/hledger/package.yaml
index bd8bf4089..c4462f5f1 100644
--- a/hledger/package.yaml
+++ b/hledger/package.yaml
@@ -117,7 +117,7 @@ library:
   - mtl
   - mtl-compat
   - old-time
-  - megaparsec >=5
+  - megaparsec >=5 && < 5.1
   - regex-tdfa
   - safe >=0.2
   - split >=0.1 && <0.3