postcss
diff --git a/‎lib/map-generator.js‎
Lines changed: 5 additions & 1 deletion b/‎lib/map-generator.js‎
Lines changed: 5 additions & 1 deletion
@@ -186,6 +186,10 @@ class MapGenerator {
   generateMap() {
     if (this.root) {
       this.generateString()
+    } else if (this.previous().length === 1) {
+      let prev = this.previous()[0].consumer()
+      prev.file = this.outputFile()
+      this.map = SourceMapGenerator.fromSourceMap(prev)
     } else {
       this.map = new SourceMapGenerator({ file: this.outputFile() })
       this.map.addMapping({
@@ -196,7 +200,7 @@ class MapGenerator {
     }
 
     if (this.isSourcesContent()) this.setSourcesContent()
-    if (this.previous().length > 0) this.applyPrevMaps()
+    if (this.root && this.previous().length > 0) this.applyPrevMaps()
     if (this.isAnnotation()) this.addAnnotation()
 
     if (this.isInline()) {