diff --git a/src/libImaging/Convert.c b/src/libImaging/Convert.c
index 1fa74a13b3b..9012cfcd74b 100644
--- a/src/libImaging/Convert.c
+++ b/src/libImaging/Convert.c
@@ -1595,7 +1595,7 @@ convert(
         return (Imaging)ImagingError_ValueError("conversion not supported");
 #else
         static char buf[100];
-        sprintf(buf, "conversion from %.10s to %.10s not supported", imIn->mode, mode);
+        snprintf(buf, 100, "conversion from %.10s to %.10s not supported", imIn->mode, mode);
         return (Imaging)ImagingError_ValueError(buf);
 #endif
     }
@@ -1645,8 +1645,9 @@ ImagingConvertTransparent(Imaging imIn, const char *mode, int r, int g, int b) {
 #else
     {
         static char buf[100];
-        sprintf(
+        snprintf(
             buf,
+            100,
             "conversion from %.10s to %.10s not supported in convert_transparent",
             imIn->mode,
             mode);