diff --git a/CHANGELOG.md b/CHANGELOG.md
index 26da6955..8bbc5c84 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,11 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed an initialization error when using plugin groups for plugins that are
+  installed outside of a Wine prefix.
+
 ### yabridgectl
 
 - Resolve relative paths when adding plugin directories or when changing
diff --git a/src/plugin/host-process.cpp b/src/plugin/host-process.cpp
index 9c6b9871..e8c3745c 100644
--- a/src/plugin/host-process.cpp
+++ b/src/plugin/host-process.cpp
@@ -149,8 +149,14 @@ GroupHost::GroupHost(
     // the first process will handle the connections for both yabridge
     // instances.
     const bp::environment host_env = set_wineprefix();
-    fs::path wine_prefix = host_env.at("WINEPREFIX").to_string();
-    if (host_env.at("WINEPREFIX").empty()) {
+    fs::path wine_prefix;
+    if (auto wine_prefix_envvar = host_env.find("WINEPREFIX");
+        wine_prefix_envvar != host_env.end()) {
+        // This is a bit ugly, but Boost.Process's environment does not have a
+        // graceful way to check for empty environment variables in const
+        // qualified environments
+        wine_prefix = wine_prefix_envvar->to_string();
+    } else {
         // Fall back to `~/.wine` if this has not been set or detected. This
         // would happen if the plugin's .dll file is not inside of a Wine
         // prefix. If this happens, then the Wine instance will be launched in