diff --git a/runtime/bin/file_system_watcher_macos.cc b/runtime/bin/file_system_watcher_macos.cc
index fbecffa5cfb..5c0d43077a0 100644
--- a/runtime/bin/file_system_watcher_macos.cc
+++ b/runtime/bin/file_system_watcher_macos.cc
@@ -7,7 +7,7 @@
 
 #include "bin/file_system_watcher.h"
 
-#if !defined(TARGET_OS_IOS)
+#if !TARGET_OS_IOS
 
 #include <errno.h>  // NOLINT
 #include <fcntl.h>  // NOLINT
@@ -394,7 +394,7 @@ Dart_Handle FileSystemWatcher::ReadEvents(intptr_t id, intptr_t path_id) {
 }  // namespace bin
 }  // namespace dart
 
-#else  // !defined(TARGET_OS_IOS)
+#else  // !TARGET_OS_IOS
 
 namespace dart {
 namespace bin {
@@ -432,6 +432,6 @@ intptr_t FileSystemWatcher::WatchPath(intptr_t id,
 }  // namespace bin
 }  // namespace dart
 
-#endif  // !defined(TARGET_OS_IOS)
+#endif  // !TARGET_OS_IOS
 
 #endif  // defined(TARGET_OS_MACOS)
diff --git a/runtime/bin/platform_macos.cc b/runtime/bin/platform_macos.cc
index e970d6e9572..54b48d6a071 100644
--- a/runtime/bin/platform_macos.cc
+++ b/runtime/bin/platform_macos.cc
@@ -12,9 +12,9 @@
 #include "bin/file.h"
 #include "bin/platform.h"
 
-#if !defined(TARGET_OS_IOS)
+#if !TARGET_OS_IOS
 #include <crt_externs.h>  // NOLINT
-#endif  // !defined(TARGET_OS_IOS)
+#endif  // !TARGET_OS_IOS
 #include <signal.h>  // NOLINT
 #include <string.h>  // NOLINT
 #include <unistd.h>  // NOLINT
@@ -68,7 +68,7 @@ bool Platform::LocalHostname(char *buffer, intptr_t buffer_length) {
 
 
 char** Platform::Environment(intptr_t* count) {
-#if defined(TARGET_OS_IOS)
+#if TARGET_OS_IOS
   // TODO(iposva): On Mac (desktop), _NSGetEnviron() is used to access the
   // environ from shared libraries or bundles. This is present in crt_externs.h
   // which is unavailable on iOS. On iOS, everything is statically linked for
diff --git a/runtime/bin/process_macos.cc b/runtime/bin/process_macos.cc
index bf81a8c31f6..f6949582e22 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.cc
@@ -7,7 +7,7 @@
 
 #include "bin/process.h"
 
-#if !defined(TARGET_OS_IOS)
+#if !TARGET_OS_IOS
 #include <crt_externs.h>  // NOLINT
 #endif
 #include <errno.h>  // NOLINT
@@ -451,7 +451,7 @@ class ProcessStarter {
       ReportChildError();
     }
 
-#if !defined(TARGET_OS_IOS)
+#if !TARGET_OS_IOS
     if (program_environment_ != NULL) {
       // On MacOS you have to do a bit of magic to get to the
       // environment strings.
diff --git a/runtime/platform/globals.h b/runtime/platform/globals.h
index 0d493100639..cd7b0587bab 100644
--- a/runtime/platform/globals.h
+++ b/runtime/platform/globals.h
@@ -94,8 +94,8 @@
 // TODO(iposva): Rename TARGET_OS_MACOS to TARGET_OS_MAC to inherit
 // the value defined in TargetConditionals.h
 #define TARGET_OS_MACOS 1
-#if TARGET_OS_IPHONE
-#define TARGET_OS_IOS
+#if TARGET_OS_IPHONE && !defined(TARGET_OS_IOS)
+#define TARGET_OS_IOS 1
 #endif
 
 #elif defined(_WIN32)
@@ -279,17 +279,17 @@ typedef simd128_value_t fpu_register_t;
 #elif defined(TARGET_ARCH_X64)
   // No simulator used.
 #elif defined(TARGET_ARCH_ARM)
-#if !defined(HOST_ARCH_ARM) || defined(TARGET_OS_IOS)
+#if !defined(HOST_ARCH_ARM) || TARGET_OS_IOS
 #define USING_SIMULATOR 1
 #endif
 
 #elif defined(TARGET_ARCH_ARM64)
-#if !defined(HOST_ARCH_ARM64) || defined(TARGET_OS_IOS)
+#if !defined(HOST_ARCH_ARM64) || TARGET_OS_IOS
 #define USING_SIMULATOR 1
 #endif
 
 #elif defined(TARGET_ARCH_MIPS)
-#if !defined(HOST_ARCH_MIPS) || defined(TARGET_OS_IOS)
+#if !defined(HOST_ARCH_MIPS) || TARGET_OS_IOS
 #define USING_SIMULATOR 1
 #endif
 
diff --git a/runtime/vm/os_macos.cc b/runtime/vm/os_macos.cc
index a447e4187e6..aed5d33529b 100644
--- a/runtime/vm/os_macos.cc
+++ b/runtime/vm/os_macos.cc
@@ -15,7 +15,7 @@
 #include <sys/time.h>  // NOLINT
 #include <sys/resource.h>  // NOLINT
 #include <unistd.h>  // NOLINT
-#if defined(TARGET_OS_IOS)
+#if TARGET_OS_IOS
 #include <sys/sysctl.h>
 #endif
 
@@ -86,7 +86,7 @@ int64_t OS::GetCurrentTimeMicros() {
 
 
 int64_t OS::GetCurrentTraceMicros() {
-#if defined(TARGET_OS_IOS)
+#if TARGET_OS_IOS
   // On iOS mach_absolute_time stops while the device is sleeping. Instead use
   // now - KERN_BOOTTIME to get a time difference that is not impacted by clock
   // changes. KERN_BOOTTIME will be updated by the system whenever the system
@@ -118,7 +118,7 @@ int64_t OS::GetCurrentTraceMicros() {
   result *= timebase_info.numer;
   result /= timebase_info.denom;
   return result;
-#endif  // defined(TARGET_OS_IOS)
+#endif  // TARGET_OS_IOS
 }