diff --git a/src/interfaces/ecpg/ecpglib/data.c b/src/interfaces/ecpg/ecpglib/data.c
index d486bb9c29..bdc90eda6f 100644
--- a/src/interfaces/ecpg/ecpglib/data.c
+++ b/src/interfaces/ecpg/ecpglib/data.c
@@ -59,7 +59,7 @@ garbage_left(enum ARRAY_TYPE isarray, char **scan_length, enum COMPAT_MODE compa
 			/* skip invalid characters */
 			do {
 				(*scan_length)++;
-			} while (isdigit(**scan_length));
+			} while (isdigit((unsigned char) **scan_length));
 		}
 
 		if (**scan_length != ' ' && **scan_length != '\0')