diff --git a/var/spack/repos/builtin/packages/macsio/cast.patch b/var/spack/repos/builtin/packages/macsio/cast.patch
new file mode 100644
index 00000000000..5d26d8ebac7
--- /dev/null
+++ b/var/spack/repos/builtin/packages/macsio/cast.patch
@@ -0,0 +1,11 @@
+--- spack-src/plugins/macsio_silo.c.org	2020-02-04 10:48:08.031770849 +0900
++++ spack-src/plugins/macsio_silo.c	2020-02-04 10:48:48.175592435 +0900
+@@ -706,7 +706,7 @@
+     char fileName[256];
+     MACSIO_MIF_baton_t *bat;
+     MACSIO_MIF_ioFlags_t ioFlags = {MACSIO_MIF_WRITE,
+-        JsonGetInt(main_obj, "clargs/exercise_scr")&0x1};
++        (unsigned int)JsonGetInt(main_obj, "clargs/exercise_scr")&0x1};
+ 
+     /* Without this barrier, I get strange behavior with Silo's MACSIO_MIF interface */
+ //#warning CONFIRM THIS IS STILL NEEDED
diff --git a/var/spack/repos/builtin/packages/macsio/package.py b/var/spack/repos/builtin/packages/macsio/package.py
index 579fabda7ee..46dccab4be0 100644
--- a/var/spack/repos/builtin/packages/macsio/package.py
+++ b/var/spack/repos/builtin/packages/macsio/package.py
@@ -42,6 +42,9 @@ class Macsio(CMakePackage):
     depends_on('typhonio', when="+typhonio")
     depends_on('scr', when="+scr")
 
+    # Ref: https://github.com/LLNL/MACSio/commit/51b8c40cd9813adec5dd4dd6cee948bb9ddb7ee1
+    patch('cast.patch', when='@1.1')
+
     def cmake_args(self):
         spec = self.spec
         cmake_args = []