diff --git a/common_utils.sh b/common_utils.sh
index 48d6c6de..8a617037 100644
--- a/common_utils.sh
+++ b/common_utils.sh
@@ -432,10 +432,10 @@ function install_pypy {
     "ppc64le") suffix="ppc64le";;
     "s30x")    suffix="s390x";;
     "aarch64")  suffix="aarch64";;
-    *) if [ -z "$IS_OSX" ]; then
+    *) if [ -n "$IS_OSX" ]; then
             suffix = "osx64";
        else
-            echo unknown platform $PLAT; exit 1
+            echo unknown platform "$PLAT"; exit 1
        fi;;
     esac
 
diff --git a/tests/test_library_builders.sh b/tests/test_library_builders.sh
index b66cde55..21d577a4 100644
--- a/tests/test_library_builders.sh
+++ b/tests/test_library_builders.sh
@@ -50,7 +50,10 @@ if [ -z "$IS_OSX" ]; then
     suppress build_lzo
 fi
 suppress build_ragel
-suppress build_cfitsio
+if [ -z "$IS_OSX" ]; then
+    # already installed in the macOS image, so `brew install cfitsio` fails
+    suppress build_cfitsio
+fi
 suppress build_new_zlib
 suppress build_hdf5