diff --git a/config/config.go b/config/config.go
index 261c9c4ac..d356d9f42 100644
--- a/config/config.go
+++ b/config/config.go
@@ -239,34 +239,54 @@ func (c *Config) Validate() error {
 					"%s: module repeated multiple times",
 					m.Id()))
 			}
-		}
 
-		if _, ok := modules[m.Id()]; !ok {
-			// If we haven't seen this module before, check that the
-			// source has no interpolations.
-			rc, err := NewRawConfig(map[string]interface{}{
-				"root": m.Source,
-			})
-			if err != nil {
-				errs = append(errs, fmt.Errorf(
-					"%s: module source error: %s",
-					m.Id(), err))
-			} else if len(rc.Interpolations) > 0 {
-				errs = append(errs, fmt.Errorf(
-					"%s: module source cannot contain interpolations",
-					m.Id()))
-			}
-
-			// Check that the name matches our regexp
-			if !NameRegexp.Match([]byte(m.Name)) {
-				errs = append(errs, fmt.Errorf(
-					"%s: module name can only contain letters, numbers, "+
-						"dashes, and underscores",
-					m.Id()))
-			}
+			// Already seen this module, just skip it
+			continue
 		}
 
 		modules[m.Id()] = m
+
+		// Check that the source has no interpolations
+		rc, err := NewRawConfig(map[string]interface{}{
+			"root": m.Source,
+		})
+		if err != nil {
+			errs = append(errs, fmt.Errorf(
+				"%s: module source error: %s",
+				m.Id(), err))
+		} else if len(rc.Interpolations) > 0 {
+			errs = append(errs, fmt.Errorf(
+				"%s: module source cannot contain interpolations",
+				m.Id()))
+		}
+
+		// Check that the name matches our regexp
+		if !NameRegexp.Match([]byte(m.Name)) {
+			errs = append(errs, fmt.Errorf(
+				"%s: module name can only contain letters, numbers, "+
+					"dashes, and underscores",
+				m.Id()))
+		}
+
+		// Check that the configuration can all be strings
+		raw := make(map[string]interface{})
+		for k, v := range m.RawConfig.Raw {
+			var strVal string
+			if err := mapstructure.WeakDecode(v, &strVal); err != nil {
+				errs = append(errs, fmt.Errorf(
+					"%s: variable %s must be a string value",
+					m.Id(), k))
+			}
+			raw[k] = strVal
+		}
+
+		// Update the raw configuration to only contain the string values
+		m.RawConfig, err = NewRawConfig(raw)
+		if err != nil {
+			errs = append(errs, fmt.Errorf(
+				"%s: can't initialize configuration: %s",
+				m.Id(), err))
+		}
 	}
 	dupped = nil
 
diff --git a/config/config_test.go b/config/config_test.go
index 7b7348fd9..41ca569e3 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -137,6 +137,20 @@ func TestConfigValidate_moduleSourceVar(t *testing.T) {
 	}
 }
 
+func TestConfigValidate_moduleVarInt(t *testing.T) {
+	c := testConfig(t, "validate-module-var-int")
+	if err := c.Validate(); err != nil {
+		t.Fatalf("should be valid: %s", err)
+	}
+}
+
+func TestConfigValidate_moduleVarMap(t *testing.T) {
+	c := testConfig(t, "validate-module-var-map")
+	if err := c.Validate(); err == nil {
+		t.Fatal("should be invalid")
+	}
+}
+
 func TestConfigValidate_nil(t *testing.T) {
 	var c Config
 	if err := c.Validate(); err != nil {
diff --git a/config/test-fixtures/validate-module-var-int/main.tf b/config/test-fixtures/validate-module-var-int/main.tf
new file mode 100644
index 000000000..4ee76d8bc
--- /dev/null
+++ b/config/test-fixtures/validate-module-var-int/main.tf
@@ -0,0 +1,4 @@
+module "foo" {
+    source = "./foo"
+    nodes = 3
+}
diff --git a/config/test-fixtures/validate-module-var-map/main.tf b/config/test-fixtures/validate-module-var-map/main.tf
new file mode 100644
index 000000000..e3a97b7de
--- /dev/null
+++ b/config/test-fixtures/validate-module-var-map/main.tf
@@ -0,0 +1,4 @@
+module "foo" {
+    source = "./foo"
+    nodes = [1,2,3]
+}
diff --git a/terraform/terraform_test.go b/terraform/terraform_test.go
index 5373894b9..cede986f8 100644
--- a/terraform/terraform_test.go
+++ b/terraform/terraform_test.go
@@ -932,6 +932,19 @@ STATE:
 <no state>
 `
 
+const testTerraformPlanModuleVarIntStr = `
+DIFF:
+
+module.child:
+  CREATE: aws_instance.foo
+    num:  "" => "2"
+    type: "" => "aws_instance"
+
+STATE:
+
+<no state>
+`
+
 const testTerraformPlanOrphanStr = `
 DIFF: