diff --git a/pkgs/development/tools/misc/hydra/default.nix b/pkgs/development/tools/misc/hydra/default.nix
index 1688e92c8441..27ff31dae963 100644
--- a/pkgs/development/tools/misc/hydra/default.nix
+++ b/pkgs/development/tools/misc/hydra/default.nix
@@ -9,6 +9,7 @@
       rev = "9bce425c3304173548d8e822029644bb51d35263";
       sha256 = "sha256-tGzwKNW/odtAYcazWA9bPVSmVXMGKfXsqCA1UYaaxmU=";
     };
+    patches = [ ./eval.patch ];
     nix = nixVersions.unstable;
 
     tests = {
diff --git a/pkgs/development/tools/misc/hydra/eval.patch b/pkgs/development/tools/misc/hydra/eval.patch
new file mode 100644
index 000000000000..5e156be16e31
--- /dev/null
+++ b/pkgs/development/tools/misc/hydra/eval.patch
@@ -0,0 +1,34 @@
+--- a/src/hydra-eval-jobs/hydra-eval-jobs.cc
++++ b/src/hydra-eval-jobs/hydra-eval-jobs.cc
+@@ -64,11 +64,11 @@
+ 
+ static std::string queryMetaStrings(EvalState & state, DrvInfo & drv, const string & name, const string & subAttribute)
+ {
+-    Strings res;
++    list<std::string_view> res;
+     std::function<void(Value & v)> rec;
+ 
+     rec = [&](Value & v) {
+-        state.forceValue(v);
++        state.forceValue(v, noPos);
+         if (v.type() == nString)
+             res.push_back(v.string.s);
+         else if (v.isList())
+@@ -112,7 +112,7 @@
+         callFlake(state, lockedFlake, *vFlake);
+ 
+         auto vOutputs = vFlake->attrs->get(state.symbols.create("outputs"))->value;
+-        state.forceValue(*vOutputs);
++        state.forceValue(*vOutputs, noPos);
+ 
+         auto aHydraJobs = vOutputs->attrs->get(state.symbols.create("hydraJobs"));
+         if (!aHydraJobs)
+@@ -191,7 +191,7 @@
+                     state.forceList(*a->value, *a->pos);
+                     for (unsigned int n = 0; n < a->value->listSize(); ++n) {
+                         auto v = a->value->listElems()[n];
+-                        state.forceValue(*v);
++                        state.forceValue(*v, noPos);
+                         if (v->type() == nString)
+                             job["namedConstituents"].push_back(state.forceStringNoCtx(*v));
+                     }
diff --git a/pkgs/tools/package-management/nix/default.nix b/pkgs/tools/package-management/nix/default.nix
index f7bb530480cc..e080a57dc658 100644
--- a/pkgs/tools/package-management/nix/default.nix
+++ b/pkgs/tools/package-management/nix/default.nix
@@ -66,12 +66,12 @@ in lib.makeExtensible (self: {
 
   unstable = lib.lowPrio (common rec {
     version = "2.7";
-    suffix = "pre20220127_${lib.substring 0 7 src.rev}";
+    suffix = "pre20220221_${lib.substring 0 7 src.rev}";
     src = fetchFromGitHub {
       owner = "NixOS";
       repo = "nix";
-      rev = "558c4ee3e370c9f9a6ea293df54ed6914a999f1c";
-      sha256 = "sha256-hMzKQflpgf3P7OdYKSnD1VMBSnF48XSRjaNX3bUJct4=";
+      rev = "caf51729450d4c57d48ddbef8e855e9bf65f8792";
+      sha256 = "sha256-2fbza6fWPjyTyVEqWIp0jk/Z4epjSDe1u4lbEu+v7Iw=";
     };
   });
 })