diff --git a/LOG b/LOG
index 911b21e6c7..abfd2f41d5 100644
--- a/LOG
+++ b/LOG
@@ -933,3 +933,5 @@
     mats/Mf-t*, foreign.ms, foreign4.c
 - Don't install equates.h
     Mf-install.in, wininstall/*nt.wxs
+- Double FMTBUFSIZE to fix compilation with gcc-8
+    c/prim5.c
diff --git a/c/prim5.c b/c/prim5.c
index 5bee635c00..69c6bfdfa6 100644
--- a/c/prim5.c
+++ b/c/prim5.c
@@ -219,7 +219,7 @@ static ptr s_decode_float(x) ptr x; {
     return S_decode_float(FLODAT(x));
 }
 
-#define FMTBUFSIZE 60
+#define FMTBUFSIZE 120
 #define CHUNKADDRLT(x, y) (((chunkinfo *)(Scar(x)))->addr < ((chunkinfo *)(Scar(y)))->addr)
 mkmergesort(sort_chunks, merge_chunks, ptr, Snil, CHUNKADDRLT, INITCDR)