diff --git a/lint.go b/lint.go
index 8bb1faa..946936e 100644
--- a/lint.go
+++ b/lint.go
@@ -527,7 +527,10 @@
 	})
 }
 
-var allCapsRE = regexp.MustCompile(`^[A-Z0-9_]+$`)
+var (
+	allCapsRE = regexp.MustCompile(`^[A-Z0-9_]+$`)
+	anyCapsRE = regexp.MustCompile(`[A-Z]`)
+)
 
 // knownNameExceptions is a set of names that are known to be exempt from naming checks.
 // This is usually because they are constrained by having to match names in the
@@ -544,6 +547,9 @@
 	if strings.Contains(f.f.Name.Name, "_") && !strings.HasSuffix(f.f.Name.Name, "_test") {
 		f.errorf(f.f, 1, link("http://golang.org/doc/effective_go.html#package-names"), category("naming"), "don't use an underscore in package name")
 	}
+	if anyCapsRE.MatchString(f.f.Name.Name) {
+		f.errorf(f.f, 1, link("http://golang.org/doc/effective_go.html#package-names"), category("mixed-caps"), "don't use MixedCaps in package name; %s should be %s", f.f.Name.Name, strings.ToLower(f.f.Name.Name))
+	}
 
 	check := func(id *ast.Ident, thing string) {
 		if id.Name == "_" {
diff --git a/testdata/pkg-caps.go b/testdata/pkg-caps.go
new file mode 100644
index 0000000..72225d7
--- /dev/null
+++ b/testdata/pkg-caps.go
@@ -0,0 +1,4 @@
+// MixedCaps package name
+
+// Package PkgName ...
+package PkgName // MATCH /don't use MixedCaps in package name/