diff --git a/terraform/semantics.go b/terraform/semantics.go
index 21b8199e8..51c17b68a 100644
--- a/terraform/semantics.go
+++ b/terraform/semantics.go
@@ -11,6 +11,11 @@ import (
 func smcUserVariables(c *config.Config, vs map[string]string) []error {
 	var errs []error
 
+	cvs := make(map[string]*config.Variable)
+	for _, v := range c.Variables {
+		cvs[v.Name] = v
+	}
+
 	// Check that all required variables are present
 	required := make(map[string]struct{})
 	for _, v := range c.Variables {
@@ -28,6 +33,20 @@ func smcUserVariables(c *config.Config, vs map[string]string) []error {
 		}
 	}
 
+	// Check that types match up
+	for k, _ := range vs {
+		v, ok := cvs[k]
+		if !ok {
+			continue
+		}
+
+		if v.Type() != config.VariableTypeString {
+			errs = append(errs, fmt.Errorf(
+				"%s: cannot assign string value to map type",
+				k))
+		}
+	}
+
 	// TODO(mitchellh): variables that are unknown
 
 	return errs
diff --git a/terraform/semantics_test.go b/terraform/semantics_test.go
index 018f448b1..bebf8f841 100644
--- a/terraform/semantics_test.go
+++ b/terraform/semantics_test.go
@@ -27,4 +27,14 @@ func TestSMCUserVariables(t *testing.T) {
 	if len(errs) != 0 {
 		t.Fatalf("err: %#v", errs)
 	}
+
+	// Mapping complete override
+	errs = smcUserVariables(c, map[string]string{
+		"foo": "bar",
+		"map": "baz",
+	})
+	if len(errs) == 0 {
+		t.Fatal("should have errors")
+	}
+
 }