diff --git a/errcheck/errcheck.go b/errcheck/errcheck.go
index 74bfaf0..163e345 100644
--- a/errcheck/errcheck.go
+++ b/errcheck/errcheck.go
@@ -187,6 +187,9 @@ type Checker struct {
 
 	// Tags are a list of build tags to use.
 	Tags []string
+
+	// The mod flag for go build.
+	Mod string
 }
 
 // loadPackages is used for testing.
@@ -197,10 +200,14 @@ var loadPackages = func(cfg *packages.Config, paths ...string) ([]*packages.Pack
 // LoadPackages loads all the packages in all the paths provided. It uses the
 // exclusions and build tags provided to by the user when loading the packages.
 func (c *Checker) LoadPackages(paths ...string) ([]*packages.Package, error) {
+	buildFlags := []string{fmtTags(c.Tags)}
+	if c.Mod != "" {
+		buildFlags = append(buildFlags, fmt.Sprintf("-mod=%s", c.Mod))
+	}
 	cfg := &packages.Config{
 		Mode:       packages.LoadAllSyntax,
 		Tests:      !c.Exclusions.TestFiles,
-		BuildFlags: []string{fmtTags(c.Tags)},
+		BuildFlags: buildFlags,
 	}
 	return loadPackages(cfg, paths...)
 }
diff --git a/errcheck/errcheck_test.go b/errcheck/errcheck_test.go
index 472c023..6cecc84 100644
--- a/errcheck/errcheck_test.go
+++ b/errcheck/errcheck_test.go
@@ -364,6 +364,7 @@ require github.com/testlog v0.0.0
 	cases := []struct {
 		withoutGeneratedCode bool
 		numExpectedErrs      int
+		withModVendor        bool
 	}{
 		// basic case has one error
 		{
@@ -375,16 +376,32 @@ require github.com/testlog v0.0.0
 			withoutGeneratedCode: true,
 			numExpectedErrs:      0,
 		},
+		// using checker.Mod="vendor"
+		{
+			withoutGeneratedCode: false,
+			numExpectedErrs:      1,
+			withModVendor:        true,
+		},
 	}
 
 	for i, test := range cases {
 		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
 			var checker Checker
 			checker.Exclusions.GeneratedFiles = test.withoutGeneratedCode
+			if test.withModVendor {
+				if os.Getenv("GO111MODULE") == "off" {
+					t.Skip("-mod=vendor doesn't work if modules are disabled")
+				}
+				checker.Mod = "vendor"
+			}
 			loadPackages = func(cfg *packages.Config, paths ...string) ([]*packages.Package, error) {
 				cfg.Env = append(os.Environ(),
-					"GOPATH="+tmpGopath,
-					"GOFLAGS=-mod=vendor")
+					"GOPATH="+tmpGopath)
+
+				if !test.withModVendor {
+					cfg.Env = append(cfg.Env,
+						"GOFLAGS=-mod=vendor")
+				}
 				cfg.Dir = testVendorDir
 				pkgs, err := packages.Load(cfg, paths...)
 				return pkgs, err
diff --git a/main.go b/main.go
index 6369927..641aa54 100644
--- a/main.go
+++ b/main.go
@@ -201,6 +201,8 @@ func parseFlags(checker *errcheck.Checker, args []string) ([]string, int) {
 	var excludeOnly bool
 	flags.BoolVar(&excludeOnly, "excludeonly", false, "Use only excludes from -exclude file")
 
+	flags.StringVar(&checker.Mod, "mod", "", "module download mode to use: readonly or vendor. See 'go help modules' for more.")
+
 	if err := flags.Parse(args[1:]); err != nil {
 		return nil, exitFatalError
 	}