diff --git a/refactor/importgraph/graph.go b/refactor/importgraph/graph.go
index df73e2378a..8ad8014ca5 100644
--- a/refactor/importgraph/graph.go
+++ b/refactor/importgraph/graph.go
@@ -54,7 +54,8 @@ func (g Graph) Search(roots ...string) map[string]bool {
 // Build scans the specified Go workspace and builds the forward and
 // reverse import dependency graphs for all its packages.
 // It also returns a mapping from import paths to errors for packages
-// that could not be loaded.
+// whose loading was not entirely successful.
+// A package may appear in the graph and in the errors mapping.
 func Build(ctxt *build.Context) (forward, reverse Graph, errors map[string]error) {
 	type importEdge struct {
 		from, to string
@@ -75,22 +76,26 @@ func Build(ctxt *build.Context) (forward, reverse Graph, errors map[string]error
 				ch <- pathError{path, err}
 				return
 			}
+
 			bp, err := ctxt.Import(path, "", 0)
-			if _, ok := err.(*build.NoGoError); ok {
-				return // empty directory is not an error
-			}
 			if err != nil {
-				ch <- pathError{path, err}
-				return
+				if _, ok := err.(*build.NoGoError); ok {
+					// empty directory is not an error
+				} else {
+					ch <- pathError{path, err}
+				}
+				// Even in error cases, Import usually returns a package.
 			}
-			for _, imp := range bp.Imports {
-				ch <- importEdge{path, imp}
-			}
-			for _, imp := range bp.TestImports {
-				ch <- importEdge{path, imp}
-			}
-			for _, imp := range bp.XTestImports {
-				ch <- importEdge{path, imp}
+			if bp != nil {
+				for _, imp := range bp.Imports {
+					ch <- importEdge{path, imp}
+				}
+				for _, imp := range bp.TestImports {
+					ch <- importEdge{path, imp}
+				}
+				for _, imp := range bp.XTestImports {
+					ch <- importEdge{path, imp}
+				}
 			}
 		}()
 	})
diff --git a/refactor/rename/mvpkg.go b/refactor/rename/mvpkg.go
index e31166da81..9cc743d6dd 100644
--- a/refactor/rename/mvpkg.go
+++ b/refactor/rename/mvpkg.go
@@ -61,11 +61,12 @@ func Move(ctxt *build.Context, from, to, moveTmpl string) error {
 	// Build the import graph and figure out which packages to update.
 	fwd, rev, errors := importgraph.Build(ctxt)
 	if len(errors) > 0 {
+		// With a large GOPATH tree, errors are inevitable.
+		// Report them but proceed.
 		fmt.Fprintf(os.Stderr, "While scanning Go workspace:\n")
 		for path, err := range errors {
 			fmt.Fprintf(os.Stderr, "Package %q: %s.\n", path, err)
 		}
-		return fmt.Errorf("failed to construct import graph")
 	}
 
 	// Determine the affected packages---the set of packages whose import
diff --git a/refactor/rename/rename.go b/refactor/rename/rename.go
index c115012f73..a028c21b0e 100644
--- a/refactor/rename/rename.go
+++ b/refactor/rename/rename.go
@@ -254,6 +254,8 @@ func Main(ctxt *build.Context, offsetFlag, fromFlag, to string) error {
 		// Scan the workspace and build the import graph.
 		_, rev, errors := importgraph.Build(ctxt)
 		if len(errors) > 0 {
+			// With a large GOPATH tree, errors are inevitable.
+			// Report them but proceed.
 			fmt.Fprintf(os.Stderr, "While scanning Go workspace:\n")
 			for path, err := range errors {
 				fmt.Fprintf(os.Stderr, "Package %q: %s.\n", path, err)