diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..5f3c68e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+nimcache/
+
diff --git a/.travis.yml b/.travis.yml
index 9ee1b9e..4be80bc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,9 +9,15 @@ git:
   # when multiple CI builds are queued, the tested commit needs to be in the last X commits cloned with "--depth X"
   depth: 10
 
-os:
-  - linux
-  - osx
+matrix:
+  include:
+    - os: linux
+      arch: amd64
+      sudo: required
+    - os: linux
+      arch: arm64
+      sudo: required
+    - os: osx
 
 install:
   # build nim from our own branch - this to avoid the day-to-day churn and
diff --git a/bearssl/decls.nim b/bearssl/decls.nim
index b536f0f..e137954 100644
--- a/bearssl/decls.nim
+++ b/bearssl/decls.nim
@@ -49,7 +49,8 @@ else:
 
 when sizeof(int) == 8:
   {.passC: "-DBR_64=1".}
-  {.passC:" -DBR_amd64=1".}
+  when hostCPU == "amd64":
+    {.passC:" -DBR_amd64=1".}
   when defined(vcc):
     {.passC: "-DBR_UMUL128=1".}
   else: