diff --git a/src/libexpr/flake/flakeref.cc b/src/libexpr/flake/flakeref.cc
index f7ef19b3f..93ad33a33 100644
--- a/src/libexpr/flake/flakeref.cc
+++ b/src/libexpr/flake/flakeref.cc
@@ -289,4 +289,6 @@ std::tuple<FlakeRef, std::string, ExtendedOutputsSpec> parseFlakeRefWithFragment
     return {std::move(flakeRef), fragment, std::move(extendedOutputsSpec)};
 }
 
+std::regex flakeIdRegex(flakeIdRegexS, std::regex::ECMAScript);
+
 }
diff --git a/src/libexpr/flake/flakeref.hh b/src/libexpr/flake/flakeref.hh
index a7c9208c0..ffb2e50de 100644
--- a/src/libexpr/flake/flakeref.hh
+++ b/src/libexpr/flake/flakeref.hh
@@ -6,6 +6,7 @@
 #include "fetchers.hh"
 #include "outputs-spec.hh"
 
+#include <regex>
 #include <variant>
 
 namespace nix {
@@ -91,5 +92,7 @@ std::tuple<FlakeRef, std::string, ExtendedOutputsSpec> parseFlakeRefWithFragment
     bool allowMissing = false,
     bool isFlake = true);
 
+const static std::string flakeIdRegexS = "[a-zA-Z][a-zA-Z0-9_-]*";
+extern std::regex flakeIdRegex;
 
 }
diff --git a/src/libutil/url-parts.hh b/src/libutil/url-parts.hh
index 98162b0f7..4712c0c91 100644
--- a/src/libutil/url-parts.hh
+++ b/src/libutil/url-parts.hh
@@ -41,7 +41,4 @@ extern std::regex revRegex;
 /// A ref or revision, or a ref followed by a revision.
 const static std::string refAndOrRevRegex = "(?:(" + revRegexS + ")|(?:(" + refRegexS + ")(?:/(" + revRegexS + "))?))";
 
-const static std::string flakeIdRegexS = "[a-zA-Z][a-zA-Z0-9_-]*";
-extern std::regex flakeIdRegex;
-
 }
diff --git a/src/libutil/url.cc b/src/libutil/url.cc
index e700c8eaf..2970f8d2d 100644
--- a/src/libutil/url.cc
+++ b/src/libutil/url.cc
@@ -8,7 +8,6 @@ namespace nix {
 std::regex refRegex(refRegexS, std::regex::ECMAScript);
 std::regex badGitRefRegex(badGitRefRegexS, std::regex::ECMAScript);
 std::regex revRegex(revRegexS, std::regex::ECMAScript);
-std::regex flakeIdRegex(flakeIdRegexS, std::regex::ECMAScript);
 
 ParsedURL parseURL(const std::string & url)
 {