diff --git a/docs/ios/build_instructions.md b/docs/ios/build_instructions.md
index 60e943f..1d0c76a 100644
--- a/docs/ios/build_instructions.md
+++ b/docs/ios/build_instructions.md
@@ -12,7 +12,7 @@
 
 ## System requirements
 
-* A 64-bit Mac running 10.11+.
+* A 64-bit Mac running 10.12.6 or later.
 * [Xcode](https://developer.apple.com/xcode) 9.0+.
 * The current version of the JDK (required for the Closure compiler).
 
@@ -226,6 +226,10 @@
 $ out/Debug-iphonesimulator/iossim out/Debug-iphonesimulator/Chromium.app
 ```
 
+With Xcode 9, `iossim` no longer automatically launches the Simulator. This must now
+be done manually from within Xcode (`Xcode > Open Developer Tool > Simulator`), and
+also must be done *after* running `iossim`.
+
 ### Passing arguments
 
 Arguments needed to be passed to the test application through `iossim`, such as