diff --git a/ChangeLog b/ChangeLog
index ba59c533..2c16fdd7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -19,6 +19,7 @@
 - add missing flushes on write to target [harukizaemon]
 - hide info messages you could get with some older glibs [kleisauke]
 - fix --no-strip on dzsave with icc-profiles [altert]
+- better GraphicsMagick image write [bfriesen]
 
 6/9/20 started 8.10.2
 - update magicksave/load profile handling [kelilevi]
diff --git a/libvips/foreign/heifload.c b/libvips/foreign/heifload.c
index 5b0b7160..9b3232db 100644
--- a/libvips/foreign/heifload.c
+++ b/libvips/foreign/heifload.c
@@ -987,11 +987,15 @@ 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;
 		}
 	}
 
diff --git a/libvips/foreign/spngload.c b/libvips/foreign/spngload.c
index baba7a4a..b3e6a601 100644
--- a/libvips/foreign/spngload.c
+++ b/libvips/foreign/spngload.c
@@ -94,13 +94,18 @@ vips_foreign_load_png_stream( spng_ctx *ctx, void *user,
 {
 	VipsSource *source = VIPS_SOURCE( user );
 
-	gint64 bytes_read;
+	while( length > 0 ) {
+		gint64 bytes_read;
 
-	bytes_read = vips_source_read( source, dest, length );
-	if( bytes_read < 0 )
-		return( SPNG_IO_ERROR );
-	if( bytes_read < length )
-		return( SPNG_IO_EOF);
+		bytes_read = vips_source_read( source, dest, length );
+		if( bytes_read < 0 )
+			return( SPNG_IO_ERROR );
+		if( bytes_read == 0 )
+			return( SPNG_IO_EOF );
+
+		dest += bytes_read;
+		length -= bytes_read;
+	}
 
 	return( 0 );
 }