diff --git a/format.cc b/format.cc
index bbc9b423..568c8ce8 100644
--- a/format.cc
+++ b/format.cc
@@ -51,6 +51,7 @@ using fmt::StringRef;
 #if _MSC_VER
 # undef snprintf
 # define snprintf _snprintf
+# define isinf(x) (!_finite(x))
 #endif
 
 namespace {