diff --git a/.ci/bazel-3.7.2-darwin-x86_64.sha256 b/.ci/bazel-3.7.2-darwin-x86_64.sha256
deleted file mode 100644
index 7ac61c4ff..000000000
--- a/.ci/bazel-3.7.2-darwin-x86_64.sha256
+++ /dev/null
@@ -1 +0,0 @@
-80c82e93a12ba30021692b11c78007807e82383a673be1602573b944beb359ab  bazel-3.7.2-darwin-x86_64
diff --git a/.ci/bazel-3.7.2-linux-x86_64.sha256 b/.ci/bazel-3.7.2-linux-x86_64.sha256
deleted file mode 100644
index 64c1c3ff3..000000000
--- a/.ci/bazel-3.7.2-linux-x86_64.sha256
+++ /dev/null
@@ -1 +0,0 @@
-70dc0bee198a4c3d332925a32d464d9036a831977501f66d4996854ad4e4fc0d  bazel-3.7.2-linux-x86_64
diff --git a/.ci/bazel-3.7.2-windows-x86_64.exe.sha256 b/.ci/bazel-3.7.2-windows-x86_64.exe.sha256
deleted file mode 100644
index eed5a9d82..000000000
--- a/.ci/bazel-3.7.2-windows-x86_64.exe.sha256
+++ /dev/null
@@ -1 +0,0 @@
-ecb696b1b9c9da6728d92fbfe8410bafb4b3a65c358980e49742233f33f74d10  bazel-3.7.2-windows-x86_64.exe
diff --git a/.ci/bazel-4.0.0-darwin-x86_64.sha256 b/.ci/bazel-4.0.0-darwin-x86_64.sha256
new file mode 100644
index 000000000..fc47cac96
--- /dev/null
+++ b/.ci/bazel-4.0.0-darwin-x86_64.sha256
@@ -0,0 +1 @@
+349f3c9dd24191369c1073c57cc1386fc3c2d4ad7d44135c3d873c9dc67fae1f  bazel-4.0.0-darwin-x86_64
diff --git a/.ci/bazel-4.0.0-linux-x86_64.sha256 b/.ci/bazel-4.0.0-linux-x86_64.sha256
new file mode 100644
index 000000000..106524c6d
--- /dev/null
+++ b/.ci/bazel-4.0.0-linux-x86_64.sha256
@@ -0,0 +1 @@
+7bee349a626281fc8b8d04a7a0b0358492712377400ab12533aeb39c2eb2b901  bazel-4.0.0-linux-x86_64
diff --git a/.ci/bazel-4.0.0-windows-x86_64.exe.sha256 b/.ci/bazel-4.0.0-windows-x86_64.exe.sha256
new file mode 100644
index 000000000..8aeb31f57
--- /dev/null
+++ b/.ci/bazel-4.0.0-windows-x86_64.exe.sha256
@@ -0,0 +1 @@
+43930bbbc8b5d618884ee8145e1ec181760bf9eea42d16217a30381d176e4cf6  bazel-4.0.0-windows-x86_64.exe
diff --git a/.ci/bazelversion b/.ci/bazelversion
index 0b2eb36f5..fcdb2e109 100644
--- a/.ci/bazelversion
+++ b/.ci/bazelversion
@@ -1 +1 @@
-3.7.2
+4.0.0
diff --git a/haskell/private/versions.bzl b/haskell/private/versions.bzl
index 4d9c6621c..0167bebf3 100644
--- a/haskell/private/versions.bzl
+++ b/haskell/private/versions.bzl
@@ -45,7 +45,7 @@ def check_version(actual_version):
     # Please use length 3 tuples, because bazel versions has 3 members;
     # to avoid surprising behaviors (for example (2,0) >/= (2, 0, 0))
     min_bazel = (2, 1, 0)  # Change THIS LINE when changing bazel min version
-    max_bazel = (3, 7, 2)  # Change THIS LINE when changing bazel max version
+    max_bazel = (4, 0, 0)  # Change THIS LINE when changing bazel max version
 
     actual = tuple(_parse_bazel_version(actual_version))
 
diff --git a/nixpkgs/default.nix b/nixpkgs/default.nix
index d290e5352..a9a8e927a 100644
--- a/nixpkgs/default.nix
+++ b/nixpkgs/default.nix
@@ -1,7 +1,7 @@
 let
-  # 2021-02-04
-  sha256 = "1bkjh566r1bpbddz6fjhccn872p1dlvg5fwq9j2qdj4b5q2pmljc";
-  rev = "24e5fe6075bc7a137bb701eb8a378f5a8689e10d";
+  # 2021-02-19
+  sha256 = "1fwl898f6wznkjpwq11brgadz6iff5w5f4lwj2l7ax2rz7r03mnn";
+  rev = "ad4db3f4d8ae54482c63c31c14921cb73953548d";
 in
 import (fetchTarball {
   inherit sha256;
diff --git a/shell.nix b/shell.nix
index 78d394014..9d6a1f86c 100644
--- a/shell.nix
+++ b/shell.nix
@@ -17,7 +17,7 @@ mkShell {
     which
     perl
     python3
-    bazel
+    bazel_4
     jdk11
     # For stack_install.
     stack
@@ -49,6 +49,6 @@ mkShell {
     fi
 
     # source bazel bash completion
-    source ${pkgs.bazel}/share/bash-completion/completions/bazel.bash
+    source ${bazel_4}/share/bash-completion/completions/bazel.bash
   '';
 }
diff --git a/start b/start
index eecbd76b3..11a40d4ea 100755
--- a/start
+++ b/start
@@ -6,8 +6,8 @@
 MIN_BAZEL_MAJOR=2
 MIN_BAZEL_MINOR=1
 
-MAX_BAZEL_MAJOR=3
-MAX_BAZEL_MINOR=7
+MAX_BAZEL_MAJOR=4
+MAX_BAZEL_MINOR=0
 
 set -e