diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3f8f6a2db..5792033c1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -590,6 +590,9 @@ set (wsjt_FSRCS
   lib/zplot9.f90
   )
 
+# temporary workaround for a gfortran v7.3 ICE on Fedora 27 64-bit
+set_source_files_properties (lib/slasubs.f PROPERTIES COMPILE_FLAGS -O2)
+
 set (ka9q_CSRCS
   lib/ftrsd/decode_rs.c
   lib/ftrsd/encode_rs.c