diff --git a/stack-ghc-9.12.4.yaml b/stack-ghc-9.12.4.yaml
index 0b771a2558..f823fc7ca3 100644
--- a/stack-ghc-9.12.4.yaml
+++ b/stack-ghc-9.12.4.yaml
@@ -1,6 +1,7 @@
 # This is an experimental project-level configuration, to see if Stack can be
 # built with GHC 9.12.4.
 snapshot: nightly-2026-07-02 # GHC 9.12.4
+compiler-check: match-exact # Protect against RCs of GHC 9.12.5
 
 extra-deps:
 # nightly-2026-07-02 specifies Cabal-3.14.2.0
@@ -18,8 +19,8 @@ docker:
 nix:
   # --nix on the command-line to enable.
   packages:
+  - pkg-config
   - zlib
-  - unzip
 
 flags:
   stack:
diff --git a/stack-ghc-9.12.5.yaml b/stack-ghc-9.12.5.yaml
index 9335770dba..9c9931931e 100644
--- a/stack-ghc-9.12.5.yaml
+++ b/stack-ghc-9.12.5.yaml
@@ -22,8 +22,8 @@ docker:
 nix:
   # --nix on the command-line to enable.
   packages:
+  - pkg-config
   - zlib
-  - unzip
 
 flags:
   stack:
diff --git a/stack-ghc-9.14.1.yaml b/stack-ghc-9.14.1.yaml
index 5be66cfbb3..6e9de75f2e 100644
--- a/stack-ghc-9.14.1.yaml
+++ b/stack-ghc-9.14.1.yaml
@@ -19,8 +19,8 @@ docker:
 nix:
   # --nix on the command-line to enable.
   packages:
+  - pkg-config
   - zlib
-  - unzip
 
 flags:
   stack:
diff --git a/stack.yaml b/stack.yaml
index 05fbb5c378..8cf7acdaf5 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -62,8 +62,8 @@ docker:
 nix:
   # --nix on the command-line to enable.
   packages:
+  - pkg-config
   - zlib
-  - unzip
 
 flags:
   stack: