diff --git a/examples/peerconnection/client/main_wnd.h b/examples/peerconnection/client/main_wnd.h
index f3ed2f5..8edf81f 100644
--- a/examples/peerconnection/client/main_wnd.h
+++ b/examples/peerconnection/client/main_wnd.h
@@ -20,7 +20,9 @@
 #include "examples/peerconnection/client/peer_connection_client.h"
 #include "media/base/mediachannel.h"
 #include "media/base/videocommon.h"
+#if defined(WEBRTC_WIN)
 #include "rtc_base/win32.h"
+#endif  // WEBRTC_WIN
 
 class MainWndCallback {
  public:
diff --git a/media/engine/webrtcvideocapturer.cc b/media/engine/webrtcvideocapturer.cc
index cf9eab6..5bc3f46 100644
--- a/media/engine/webrtcvideocapturer.cc
+++ b/media/engine/webrtcvideocapturer.cc
@@ -20,7 +20,10 @@
 #include "rtc_base/timeutils.h"
 
 #include "modules/video_capture/video_capture_factory.h"
+
+#if defined(WEBRTC_WIN)
 #include "rtc_base/win32.h"  // Need this to #include the impl files.
+#endif  // WEBRTC_WIN
 #include "system_wrappers/include/field_trial.h"
 
 namespace cricket {
diff --git a/rtc_base/ipaddress.cc b/rtc_base/ipaddress.cc
index 42a7fd6..a31680d 100644
--- a/rtc_base/ipaddress.cc
+++ b/rtc_base/ipaddress.cc
@@ -31,7 +31,10 @@
 #include "rtc_base/logging.h"
 #include "rtc_base/nethelpers.h"
 #include "rtc_base/stringutils.h"
+
+#if defined(WEBRTC_WIN)
 #include "rtc_base/win32.h"
+#endif  // WEBRTC_WIN
 
 namespace rtc {
 
diff --git a/rtc_base/openssladapter.cc b/rtc_base/openssladapter.cc
index 7f62bcc..ca5984a 100644
--- a/rtc_base/openssladapter.cc
+++ b/rtc_base/openssladapter.cc
@@ -14,8 +14,10 @@
 #include <unistd.h>
 #endif
 
+#if defined(WEBRTC_WIN)
 // Must be included first before openssl headers.
 #include "rtc_base/win32.h"  // NOLINT
+#endif  // WEBRTC_WIN
 
 #include <openssl/bio.h>
 #include <openssl/crypto.h>
diff --git a/rtc_base/opensslidentity.cc b/rtc_base/opensslidentity.cc
index 726ae3b..477a0e6 100644
--- a/rtc_base/opensslidentity.cc
+++ b/rtc_base/opensslidentity.cc
@@ -12,8 +12,10 @@
 
 #include <memory>
 
+#if defined(WEBRTC_WIN)
 // Must be included first before openssl headers.
 #include "rtc_base/win32.h"  // NOLINT
+#endif  // WEBRTC_WIN
 
 #include <openssl/bio.h>
 #include <openssl/bn.h>
diff --git a/rtc_base/win32.h b/rtc_base/win32.h
index 0cbc412..78f66a7 100644
--- a/rtc_base/win32.h
+++ b/rtc_base/win32.h
@@ -11,7 +11,9 @@
 #ifndef RTC_BASE_WIN32_H_
 #define RTC_BASE_WIN32_H_
 
-#if defined(WEBRTC_WIN)
+#ifndef WEBRTC_WIN
+#error "Only #include this header in Windows builds"
+#endif
 
 #ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
@@ -83,5 +85,4 @@
 
 }  // namespace rtc
 
-#endif  // WEBRTC_WIN
 #endif  // RTC_BASE_WIN32_H_