diff --git a/tools/lsp/nix/sources.json b/tools/lsp/nix/sources.json
index fc8f1eea1..56806cdd8 100644
--- a/tools/lsp/nix/sources.json
+++ b/tools/lsp/nix/sources.json
@@ -1,16 +1,4 @@
 {
-    "haskell.nix": {
-        "branch": "master",
-        "description": "Alternative Haskell Infrastructure for Nixpkgs",
-        "homepage": "https://input-output-hk.github.io/haskell.nix",
-        "owner": "input-output-hk",
-        "repo": "haskell.nix",
-        "rev": "db409cf3a0b10a7309a8102bb6a00d8870b9c67e",
-        "sha256": "0j4grhzfrd966cwni9glycdjivzmb45dga4hqhwniajc6kdyj0h4",
-        "type": "tarball",
-        "url": "https://github.com/input-output-hk/haskell.nix/archive/db409cf3a0b10a7309a8102bb6a00d8870b9c67e.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
     "nix-npm-buildpackage": {
         "branch": "master",
         "description": "Build nix packages that use npm/yarn",
@@ -23,16 +11,28 @@
         "url": "https://github.com/serokell/nix-npm-buildpackage/archive/abde678d1584af0ad00477486bca26c880963a70.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
-    "nixpkgs": {
-        "branch": "release-20.03",
-        "description": "A read-only mirror of NixOS/nixpkgs tracking the released channels. Send issues and PRs to",
-        "homepage": "https://github.com/NixOS/nixpkgs",
-        "owner": "nixos",
-        "repo": "nixpkgs",
-        "rev": "252bfe0107587d40092057f338e9ffcf7bbd90cb",
-        "sha256": "1ljw98lcc04mlz6pprlgd1plinwl5q8fraakk6bx8igkiqlxaadn",
+    "haskell.nix": {
+        "branch": "master",
+        "description": "Alternative Haskell Infrastructure for Nixpkgs",
+        "homepage": "https://input-output-hk.github.io/haskell.nix",
+        "owner": "input-output-hk",
+        "repo": "haskell.nix",
+        "rev": "f4136211c933b444ab2e0f358abd223929970220",
+        "sha256": "1b9nxzkg29hwczr6pb6a7arxka8z0swzq7b2bqyxqzr4qvpcjlc1",
         "type": "tarball",
-        "url": "https://github.com/nixos/nixpkgs/archive/252bfe0107587d40092057f338e9ffcf7bbd90cb.tar.gz",
+        "url": "https://github.com/input-output-hk/haskell.nix/archive/f4136211c933b444ab2e0f358abd223929970220.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "master",
+        "description": "Pinned Nixpkgs tree (master follows nixos-unstable-small, only tags have stable history)",
+        "homepage": "",
+        "owner": "serokell",
+        "repo": "nixpkgs",
+        "rev": "ec2598d025b7670472175413748ce688a60712b9",
+        "sha256": "0b1acpgy9jbf57zxqk0zqza7yk2a70q8mrhd519rq8kmgc95dw1x",
+        "type": "tarball",
+        "url": "https://github.com/serokell/nixpkgs/archive/ec2598d025b7670472175413748ce688a60712b9.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }
diff --git a/tools/lsp/squirrel/squirrel.nix b/tools/lsp/squirrel/squirrel.nix
index d0812a31c..32907630f 100644
--- a/tools/lsp/squirrel/squirrel.nix
+++ b/tools/lsp/squirrel/squirrel.nix
@@ -15,11 +15,6 @@ let
           rm vendor/*/*
           ( cd ${grammars}; for i in *; do cp $i/parser.c $NIX_BUILD_TOP/*/vendor/$i; done )
         '';
-        configureFlags = with pkgs;
-          lib.optionals linux-static [
-            "--ghc-option=-optl=-L${zlib.static}/lib"
-            "--ghc-option=-optl=-L${nixpkgs.pkgsStatic.numactl}/lib"
-          ];
       };
     }];
   };