diff --git a/Dockerfile b/Dockerfile
index 5eeb2ae9c4..e8e3ea37c4 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -15,6 +15,10 @@ RUN sed -i \
     /usr/include/malloc.h
 
 ENV GYP_DEFINES='clang=0 use_experimental_allocator_shim=0 use_allocator=none musl=1'
+# Alpine does not support python3 yet, but depot_tools enabled python3
+# by default. Disable python3 explicitly for now.
+# See https://github.com/google/shaka-packager/issues/763 for details.
+ENV GCLIENT_PY3=0
 
 # Build shaka-packager
 WORKDIR shaka_packager
diff --git a/packager/testing/dockers/Alpine_Dockerfile b/packager/testing/dockers/Alpine_Dockerfile
index a4dcfd3386..5a0aa2b3f8 100644
--- a/packager/testing/dockers/Alpine_Dockerfile
+++ b/packager/testing/dockers/Alpine_Dockerfile
@@ -16,6 +16,10 @@ RUN sed -i \
     /usr/include/malloc.h
 
 ENV GYP_DEFINES='clang=0 use_experimental_allocator_shim=0 use_allocator=none musl=1'
+# Alpine does not support python3 yet, but depot_tools enabled python3
+# by default. Disable python3 explicitly for now.
+# See https://github.com/google/shaka-packager/issues/763 for details.
+ENV GCLIENT_PY3=0
 
 # Build and run this docker by mapping shaka-packager with
 # -v "shaka-packager:/shaka-packager".