diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index 6c089469dc93b1687101dd1e4e2ad60d063c6e09..699ec0b99625a603a5d9ecc70ddcf75ba2a540ef 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -54,7 +54,7 @@ BuildEnvironment readEnvironment(const Path & path)
         R"re((?:[a-zA-Z_][a-zA-Z0-9_]*))re";
 
     static std::string simpleStringRegex =
-        R"re((?:[a-zA-Z0-9_/:\.\-\+=]*))re";
+        R"re((?:[a-zA-Z0-9_/:\.\-\+=@%]*))re";
 
     static std::string dquotedStringRegex =
         R"re((?:\$?"(?:[^"\\]|\\[$`"\\\n])*"))re";
diff --git a/tests/shell.nix b/tests/shell.nix
index 53759f99aa2d94b8372ac9e9ca6da1e1ba419350..f174db583a0758a3e682937a532edf52aff21a62 100644
--- a/tests/shell.nix
+++ b/tests/shell.nix
@@ -34,6 +34,8 @@ let pkgs = rec {
     name = "shellDrv";
     builder = "/does/not/exist";
     VAR_FROM_NIX = "bar";
+    ASCII_PERCENT = "%";
+    ASCII_AT = "@";
     TEST_inNixShell = if inNixShell then "true" else "false";
     inherit stdenv;
     outputs = ["dev" "out"];