diff --git a/TODO b/TODO
index f2257760..b3a4177b 100644
--- a/TODO
+++ b/TODO
@@ -1,5 +1,3 @@
-- vips_system needs to use "%%" for a % character, for compatibility with 
-  vips 7.38
 
 - can we use postbuild elsewhere? look at use of "preclose" / "written", etc. 
 
diff --git a/libvips/iofuncs/system.c b/libvips/iofuncs/system.c
index 1f5cc241..1082ec1c 100644
--- a/libvips/iofuncs/system.c
+++ b/libvips/iofuncs/system.c
@@ -119,6 +119,7 @@ vips_system_build( VipsObject *object )
 	char line[VIPS_PATH_MAX];
 	char txt[VIPS_PATH_MAX];
 	VipsBuf buf = VIPS_BUF_STATIC( txt );
+	char *p;
 	int result;
 
 	if( VIPS_OBJECT_CLASS( vips_system_parent_class )->build( object ) )
@@ -164,6 +165,15 @@ vips_system_build( VipsObject *object )
 			cmd, VIPS_PATH_MAX, system->out_name ) )
 		return( -1 ); 
 
+	/* Swap all "%%" in the string for a single "%". We need this for
+	 * compatibility with older printf-based vips_system()s which
+	 * needed a double %%.
+	 */
+	for( p = cmd; *p; p++ ) 
+		if( p[0] == '%' && 
+			p[1] == '%' )
+			memmove( p, p + 1, strlen( p ) ); 
+
 	if( !(fp = vips_popenf( "%s", "r", cmd )) )
 		return( -1 );