diff --git a/2020/endoh1/README.md b/2020/endoh1/README.md
index 6b4e0f217..ac1b89b51 100644
--- a/2020/endoh1/README.md
+++ b/2020/endoh1/README.md
@@ -8,6 +8,8 @@ make
 ## To use:
 
 ```sh
+# IMPORTANT for macOS: run under Terminal.app
+
 ./prog
 ```
 
@@ -15,6 +17,7 @@ make
 ### Try:
 
 ```sh
+# IMPORTANT for macOS: run under Terminal.app
 
 # Try resizing the terminal window before the first click.
 
@@ -55,6 +58,13 @@ The submission was in violation of the "2053" size rule by one character, likely
 a late typo. It was easy to fix.
 
 
+### for macOS:
+
+We observe that this entry may not work under macOS using iTerm2.
+Users on macOS might want to run this entry run under the macOS Terminal,
+which is located in `/System/Applications/Utilities/Terminal.app`.
+
+
 ## Author's remarks:
 
 ### Semi-automatic Minesweeper: