diff --git a/lib/std/Build.zig b/lib/std/Build.zig
index ec552b98ed2bed478aef81c77c0549a12d6075aa..798729533c70421c8c5126a22540341f3129091d 100644
--- a/lib/std/Build.zig
+++ b/lib/std/Build.zig
@@ -1836,10 +1836,14 @@ fn tryFindProgram(b: *Build, full_path: []const u8) ?[]const u8 {
         if (b.graph.environ_map.get("PATHEXT")) |PATHEXT| {
             var it = mem.tokenizeScalar(u8, PATHEXT, fs.path.delimiter);
 
+            const extended_path_buf = arena.alloc(u8, full_path.len + 1 + std.process.WindowsExtension.max_len) catch @panic("OOM");
+            @memcpy(extended_path_buf[0..full_path.len], full_path);
+
             while (it.next()) |ext| {
                 if (!supportedWindowsProgramExtension(ext)) continue;
 
-                const extended_path = try mem.concat(arena, u8, &.{ full_path, ext });
+                @memcpy(extended_path_buf[full_path.len..][0..ext.len], ext);
+                const extended_path = extended_path_buf[0 .. full_path.len + ext.len];
 
                 if (Io.Dir.cwd().access(io, extended_path, .{ .execute = true })) |_| {
                     return extended_path;
@@ -2708,4 +2712,5 @@ test {
     _ = Cache;
     _ = Step;
     _ = Configuration;
+    _ = &findProgram;
 }
diff --git a/lib/std/process.zig b/lib/std/process.zig
index bcee558a65eef07afab17b484cc012326bb5004c..f3ef291763d642426770883e886c8a5a50aeae41 100644
--- a/lib/std/process.zig
+++ b/lib/std/process.zig
@@ -315,7 +315,15 @@ pub fn replacePath(io: Io, dir: Io.Dir, options: ReplaceOptions) ReplaceError {
 pub const ArgExpansion = enum { expand, no_expand };
 
 /// File name extensions supported natively by `CreateProcess()` on Windows.
-pub const WindowsExtension = enum { bat, cmd, com, exe };
+pub const WindowsExtension = enum {
+    bat,
+    cmd,
+    com,
+    exe,
+
+    /// Length of the longest supported extension (in ASCII characters)
+    pub const max_len = 3;
+};
 
 pub const SpawnError = error{
     /// The operating system does not support creating child processes.