diff --git a/src/libutil/windows/processes.cc b/src/libutil/windows/processes.cc
index cf1949aa2..a1104fa1e 100644
--- a/src/libutil/windows/processes.cc
+++ b/src/libutil/windows/processes.cc
@@ -94,7 +94,7 @@ std::string runProgram(
 Path lookupPathForProgram(const Path & program)
 {
     if (program.find('/') != program.npos || program.find('\\') != program.npos) {
-        throw Error("program '%1%' partially specifies its path", program);
+        throw UsageError("program '%1%' partially specifies its path", program);
     }
 
     // Possible extensions.
@@ -107,8 +107,9 @@ Path lookupPathForProgram(const Path & program)
     }
 
     // Look through each directory listed in $PATH.
-    for (const std::string & dir : tokenizeString<Strings>(*getEnv("PATH"), ";")) {
-        Path candidate = canonPath(dir) + '/' + program;
+    for (const std::string & dir : tokenizeString<Strings>(*path, ";")) {
+        // TODO: This should actually be canonPath(dir), but that ends up appending two drive paths
+        Path candidate = dir + "/" + program;
         for (const auto ext : exts) {
             if (pathExists(candidate + ext)) {
                 return candidate;
@@ -408,5 +409,4 @@ bool statusOk(int status)
 {
     return status == 0;
 }
-
 }
diff --git a/tests/unit/libutil/spawn.cc b/tests/unit/libutil/spawn.cc
index 6d9821f4e..e84de18f1 100644
--- a/tests/unit/libutil/spawn.cc
+++ b/tests/unit/libutil/spawn.cc
@@ -6,11 +6,19 @@ namespace nix {
 /*
 TEST(SpawnTest, spawnEcho)
 {
-auto output = runProgram(RunOptions{.program = "echo", .args = {}});
+auto output = runProgram(RunOptions{.program = "cmd", .lookupPath = true, .args = {"/C", "echo \"hello world\""}});
+std::cout << output.second << std::endl;
 }
 */
 
 #ifdef _WIN32
+Path lookupPathForProgram(const Path & program);
+TEST(SpawnTest, pathSearch)
+{
+    ASSERT_NO_THROW(lookupPathForProgram("cmd"));
+    ASSERT_NO_THROW(lookupPathForProgram("cmd.exe"));
+    ASSERT_THROW(lookupPathForProgram("C:/System32/cmd.exe"), UsageError);
+}
 std::string windowsEscape(const std::string & str, bool cmd);
 
 TEST(SpawnTest, windowsEscape)