diff --git a/internal/lsp/cache/check.go b/internal/lsp/cache/check.go
index b3e9e04df1..b578bae2a0 100644
--- a/internal/lsp/cache/check.go
+++ b/internal/lsp/cache/check.go
@@ -11,6 +11,7 @@ import (
 	"go/ast"
 	"go/token"
 	"go/types"
+	"path"
 	"sort"
 	"sync"
 
@@ -309,6 +310,24 @@ func typeCheck(ctx context.Context, fset *token.FileSet, m *metadata, mode sourc
 		},
 		Importer: importerFunc(func(pkgPath string) (*types.Package, error) {
 			dep := deps[packagePath(pkgPath)]
+			if dep == nil {
+				// We may be in GOPATH mode, in which case we need to check vendor dirs.
+				searchDir := path.Dir(pkg.PkgPath())
+				for {
+					vdir := packagePath(path.Join(searchDir, "vendor", pkgPath))
+					if vdep := deps[vdir]; vdep != nil {
+						dep = vdep
+						break
+					}
+
+					// Search until Dir doesn't take us anywhere new, e.g. "." or "/".
+					next := path.Dir(searchDir)
+					if searchDir == next {
+						break
+					}
+					searchDir = next
+				}
+			}
 			if dep == nil {
 				return nil, errors.Errorf("no package for import %s", pkgPath)
 			}
diff --git a/internal/lsp/cache/load.go b/internal/lsp/cache/load.go
index 98b083a9fe..12839d6377 100644
--- a/internal/lsp/cache/load.go
+++ b/internal/lsp/cache/load.go
@@ -42,6 +42,9 @@ func (s *snapshot) load(ctx context.Context, scopes ...interface{}) ([]*metadata
 	for _, scope := range scopes {
 		switch scope := scope.(type) {
 		case []packagePath:
+			// The only time we pass package paths is when we're doing a
+			// partial workspace load. In those cases, the paths came back from
+			// go list and should already be GOPATH-vendorized when appropriate.
 			for _, p := range scope {
 				query = append(query, string(p))
 			}
@@ -59,6 +62,8 @@ func (s *snapshot) load(ctx context.Context, scopes ...interface{}) ([]*metadata
 				q = "./..."
 			}
 			query = append(query, q)
+		default:
+			panic(fmt.Sprintf("unknown scope type %T", scope))
 		}
 	}
 	ctx, done := trace.StartSpan(ctx, "cache.view.load", telemetry.Query.Of(query))