diff --git a/libvips/foreign/heifload.c b/libvips/foreign/heifload.c
index 77e5f4bc..b4a14e56 100644
--- a/libvips/foreign/heifload.c
+++ b/libvips/foreign/heifload.c
@@ -963,11 +963,15 @@ vips_foreign_load_heif_read( void *data, size_t size, void *userdata )
 {
 	VipsForeignLoadHeif *heif = (VipsForeignLoadHeif *) userdata;
 
-	gint64 result;
+	while( size > 0 ) {
+		gint64 result;
 
-	result = vips_source_read( heif->source, data, size );
-	if( result < 0 ) 
-		return( -1 );
+		result = vips_source_read( heif->source, data, size );
+		if( result <= 0 ) 
+			return( -1 );
+
+		size -= result;
+	}
 
 	return( 0 );
 }
diff --git a/libvips/foreign/ppmload.c b/libvips/foreign/ppmload.c
index bcc2e79a..77dfbb60 100644
--- a/libvips/foreign/ppmload.c
+++ b/libvips/foreign/ppmload.c
@@ -458,13 +458,21 @@ vips_foreign_load_ppm_generate_binary( VipsRegion *or,
 	for( y = 0; y < r->height; y++ ) {
 		VipsPel *q = VIPS_REGION_ADDR( or, 0, r->top + y );
 
-		size_t bytes_read;
+		size_t n_bytes;
 
-		bytes_read = vips_source_read( ppm->source, q, sizeof_line );
-		if( bytes_read != sizeof_line ) {
-			vips_error( class->nickname, 
-				"%s", _( "file truncated" ) );
-			return( -1 );
+		n_bytes = sizeof_line;
+		while( n_bytes > 0 ) {
+			size_t bytes_read;
+
+			bytes_read = vips_source_read( ppm->source, 
+				q, sizeof_line );
+			if( bytes_read == 0 ) {
+				vips_error( class->nickname, 
+					"%s", _( "file truncated" ) );
+				return( -1 );
+			}
+
+			n_bytes -= bytes_read;
 		}
 	}