diff --git a/var/spack/repos/builtin/packages/berkeleygw/package.py b/var/spack/repos/builtin/packages/berkeleygw/package.py
index 980ebbc260..dbd1ea7fc7 100644
--- a/var/spack/repos/builtin/packages/berkeleygw/package.py
+++ b/var/spack/repos/builtin/packages/berkeleygw/package.py
@@ -232,7 +232,11 @@ def build(self, spec, prefix):
                 f90_flags += " -fallow-argument-mismatch"
             buildopts.append("COMPFLAG=-DGNU")
             buildopts.append("MOD_OPT=-J ")
-            buildopts.append("FCPP=cpp -C -nostdinc")
+            # std c11 prevents problems with linebreaks and fortran comments
+            # containing // (which is interpreted as C++ style comment)
+            buildopts.append(
+                "FCPP=%s -C -nostdinc -std=c11" % join_path(self.compiler.prefix, "bin", "cpp")
+            )
             if "+mpi" in spec:
                 buildopts.append("F90free=%s %s" % (spec["mpi"].mpifc, f90_flags))
                 buildopts.append("C_COMP=%s %s" % (spec["mpi"].mpicc, c_flags))