diff --git a/appveyor.yml b/appveyor.yml
index 5022d179e..d6f175763 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -38,7 +38,7 @@ environment:
 install:
   - if [%COMPILER%]==[clang-cl] call C:\Miniconda36-x64\Scripts\activate.bat
   - if [%COMPILER%]==[clang-cl] conda config --add channels conda-forge --force
-  - if [%COMPILER%]==[clang-cl] conda install clangdev ninja cmake
+  - if [%COMPILER%]==[clang-cl] conda install --yes clangdev ninja cmake
 
 before_build:
   - echo Running cmake...