diff --git a/Sources/Build/TestObservation.swift b/Sources/Build/TestObservation.swift
index 30001761c70..d128f4f0170 100644
--- a/Sources/Build/TestObservation.swift
+++ b/Sources/Build/TestObservation.swift
@@ -130,6 +130,8 @@ public func generateTestObservationCode(buildParameters: BuildParameters) -> Str
         #elseif os(Windows)
         @_exported import CRT
         @_exported import WinSDK
+        #elseif os(WASI)
+        @_exported import WASILibc
         #else
         @_exported import Darwin.C
         #endif
@@ -176,6 +178,8 @@ public func generateTestObservationCode(buildParameters: BuildParameters) -> Str
                                    UInt32.max, UInt32.max, &overlapped) {
                         throw ProcessLockError.unableToAquireLock(errno: Int32(GetLastError()))
                     }
+              #elseif os(WASI)
+                // WASI doesn't support flock
               #else
                 if fileDescriptor == nil {
                     let fd = open(lockFile.path, O_WRONLY | O_CREAT | O_CLOEXEC, 0o666)
@@ -201,6 +205,8 @@ public func generateTestObservationCode(buildParameters: BuildParameters) -> Str
                 overlapped.OffsetHigh = 0
                 overlapped.hEvent = nil
                 UnlockFileEx(handle, 0, UInt32.max, UInt32.max, &overlapped)
+              #elseif os(WASI)
+                // WASI doesn't support flock
               #else
                 guard let fd = fileDescriptor else { return }
                 flock(fd, LOCK_UN)
@@ -211,6 +217,8 @@ public func generateTestObservationCode(buildParameters: BuildParameters) -> Str
               #if os(Windows)
                 guard let handle = handle else { return }
                 CloseHandle(handle)
+              #elseif os(WASI)
+                // WASI doesn't support flock
               #else
                 guard let fd = fileDescriptor else { return }
                 close(fd)