diff --git a/core/config.mk b/core/config.mk
index 71c9fdc..3eddc13 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -3,6 +3,8 @@
 # current configuration and platform, which
 # are not specific to what is being built.
 
+# Only use ANDROID_BUILD_SHELL to wrap around bash.
+# DO NOT use other shells such as zsh.
 ifdef ANDROID_BUILD_SHELL
 SHELL := $(ANDROID_BUILD_SHELL)
 else
diff --git a/core/main.mk b/core/main.mk
index 3da799b..7c1ff12 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -1,3 +1,5 @@
+# Only use ANDROID_BUILD_SHELL to wrap around bash.
+# DO NOT use other shells such as zsh.
 ifdef ANDROID_BUILD_SHELL
 SHELL := $(ANDROID_BUILD_SHELL)
 else