diff --git a/third_party/lcms/src/cmsplugin.c b/third_party/lcms/src/cmsplugin.c
index b95befb..4ba998b 100644
--- a/third_party/lcms/src/cmsplugin.c
+++ b/third_party/lcms/src/cmsplugin.c
@@ -182,7 +182,9 @@ cmsBool CMSEXPORT  _cmsReadFloat32Number(cmsIOHANDLER* io, cmsFloat32Number* n)
         if (isnan(*n))
             return FALSE;
     }
-    return TRUE;
+
+    // fpclassify() required by C99
+    return (fpclassify(*n) == FP_ZERO) || (fpclassify(*n) == FP_NORMAL);
 }