diff --git a/esphome/components/api/__init__.py b/esphome/components/api/__init__.py
index b778257d66..5c15c68db7 100644
--- a/esphome/components/api/__init__.py
+++ b/esphome/components/api/__init__.py
@@ -87,7 +87,7 @@ HOMEASSISTANT_SERVICE_ACTION_SCHEMA = cv.Schema({
         cv.string: cv.string,
     }),
     cv.Optional(CONF_VARIABLES): cv.Schema({
-        cv.string: cv.lambda_,
+        cv.string: cv.returning_lambda,
     }),
 })
 
diff --git a/esphome/components/binary_sensor/__init__.py b/esphome/components/binary_sensor/__init__.py
index 336870392d..70a6ce0c58 100644
--- a/esphome/components/binary_sensor/__init__.py
+++ b/esphome/components/binary_sensor/__init__.py
@@ -70,7 +70,7 @@ def delayed_off_filter_to_code(config, filter_id):
     yield var
 
 
-@FILTER_REGISTRY.register('lambda', LambdaFilter, cv.lambda_)
+@FILTER_REGISTRY.register('lambda', LambdaFilter, cv.returning_lambda)
 def lambda_filter_to_code(config, filter_id):
     lambda_ = yield cg.process_lambda(config, [(bool, 'x')], return_type=cg.optional.template(bool))
     yield cg.new_Pvariable(filter_id, lambda_)
diff --git a/esphome/components/custom/binary_sensor/__init__.py b/esphome/components/custom/binary_sensor/__init__.py
index b08988cc5a..83b4a3dad8 100644
--- a/esphome/components/custom/binary_sensor/__init__.py
+++ b/esphome/components/custom/binary_sensor/__init__.py
@@ -8,7 +8,7 @@ CustomBinarySensorConstructor = custom_ns.class_('CustomBinarySensorConstructor'
 
 CONFIG_SCHEMA = cv.Schema({
     cv.GenerateID(): cv.declare_id(CustomBinarySensorConstructor),
-    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_LAMBDA): cv.returning_lambda,
     cv.Required(CONF_BINARY_SENSORS): cv.ensure_list(binary_sensor.BINARY_SENSOR_SCHEMA),
 })
 
diff --git a/esphome/components/custom/output/__init__.py b/esphome/components/custom/output/__init__.py
index cc4391d4ae..46abee91c8 100644
--- a/esphome/components/custom/output/__init__.py
+++ b/esphome/components/custom/output/__init__.py
@@ -9,7 +9,7 @@ CustomFloatOutputConstructor = custom_ns.class_('CustomFloatOutputConstructor')
 
 BINARY_SCHEMA = cv.Schema({
     cv.GenerateID(): cv.declare_id(CustomBinaryOutputConstructor),
-    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_LAMBDA): cv.returning_lambda,
     cv.Required(CONF_TYPE): 'binary',
     cv.Required(CONF_OUTPUTS):
         cv.ensure_list(output.BINARY_OUTPUT_SCHEMA.extend({
@@ -19,7 +19,7 @@ BINARY_SCHEMA = cv.Schema({
 
 FLOAT_SCHEMA = cv.Schema({
     cv.GenerateID(): cv.declare_id(CustomFloatOutputConstructor),
-    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_LAMBDA): cv.returning_lambda,
     cv.Required(CONF_TYPE): 'float',
     cv.Required(CONF_OUTPUTS):
         cv.ensure_list(output.FLOAT_OUTPUT_SCHEMA.extend({
diff --git a/esphome/components/custom/sensor/__init__.py b/esphome/components/custom/sensor/__init__.py
index 622d347d8a..e6da4a733c 100644
--- a/esphome/components/custom/sensor/__init__.py
+++ b/esphome/components/custom/sensor/__init__.py
@@ -8,7 +8,7 @@ CustomSensorConstructor = custom_ns.class_('CustomSensorConstructor')
 
 CONFIG_SCHEMA = cv.Schema({
     cv.GenerateID(): cv.declare_id(CustomSensorConstructor),
-    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_LAMBDA): cv.returning_lambda,
     cv.Required(CONF_SENSORS): cv.ensure_list(sensor.SENSOR_SCHEMA),
 })
 
diff --git a/esphome/components/custom/switch/__init__.py b/esphome/components/custom/switch/__init__.py
index dc5cb325bd..fd619e6769 100644
--- a/esphome/components/custom/switch/__init__.py
+++ b/esphome/components/custom/switch/__init__.py
@@ -8,7 +8,7 @@ CustomSwitchConstructor = custom_ns.class_('CustomSwitchConstructor')
 
 CONFIG_SCHEMA = cv.Schema({
     cv.GenerateID(): cv.declare_id(CustomSwitchConstructor),
-    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_LAMBDA): cv.returning_lambda,
     cv.Required(CONF_SWITCHES):
         cv.ensure_list(switch.SWITCH_SCHEMA.extend({
             cv.GenerateID(): cv.declare_id(switch.Switch),
diff --git a/esphome/components/custom/text_sensor/__init__.py b/esphome/components/custom/text_sensor/__init__.py
index 38675da142..58db2a3f9e 100644
--- a/esphome/components/custom/text_sensor/__init__.py
+++ b/esphome/components/custom/text_sensor/__init__.py
@@ -8,7 +8,7 @@ CustomTextSensorConstructor = custom_ns.class_('CustomTextSensorConstructor')
 
 CONFIG_SCHEMA = cv.Schema({
     cv.GenerateID(): cv.declare_id(CustomTextSensorConstructor),
-    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_LAMBDA): cv.returning_lambda,
     cv.Required(CONF_TEXT_SENSORS):
         cv.ensure_list(text_sensor.TEXT_SENSOR_SCHEMA.extend({
             cv.GenerateID(): cv.declare_id(text_sensor.TextSensor),
diff --git a/esphome/components/custom_component/__init__.py b/esphome/components/custom_component/__init__.py
index 0dcbb163c8..198aa6a9ec 100644
--- a/esphome/components/custom_component/__init__.py
+++ b/esphome/components/custom_component/__init__.py
@@ -8,7 +8,7 @@ CustomComponentConstructor = custom_component_ns.class_('CustomComponentConstruc
 MULTI_CONF = True
 CONFIG_SCHEMA = cv.Schema({
     cv.GenerateID(): cv.declare_id(CustomComponentConstructor),
-    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_LAMBDA): cv.returning_lambda,
     cv.Optional(CONF_COMPONENTS): cv.ensure_list(cv.Schema({
         cv.GenerateID(): cv.declare_id(cg.Component)
     }).extend(cv.COMPONENT_SCHEMA)),
diff --git a/esphome/components/sensor/__init__.py b/esphome/components/sensor/__init__.py
index 0fe0fc6bca..43f0cefd56 100644
--- a/esphome/components/sensor/__init__.py
+++ b/esphome/components/sensor/__init__.py
@@ -148,7 +148,7 @@ def exponential_moving_average_filter_to_code(config, filter_id):
     yield cg.new_Pvariable(filter_id, config[CONF_ALPHA], config[CONF_SEND_EVERY])
 
 
-@FILTER_REGISTRY.register('lambda', LambdaFilter, cv.lambda_)
+@FILTER_REGISTRY.register('lambda', LambdaFilter, cv.returning_lambda)
 def lambda_filter_to_code(config, filter_id):
     lambda_ = yield cg.process_lambda(config, [(float, 'x')],
                                       return_type=cg.optional.template(float))
diff --git a/esphome/components/template/binary_sensor/__init__.py b/esphome/components/template/binary_sensor/__init__.py
index 9c1fb549e6..14f9f23ec2 100644
--- a/esphome/components/template/binary_sensor/__init__.py
+++ b/esphome/components/template/binary_sensor/__init__.py
@@ -10,7 +10,7 @@ TemplateBinarySensor = template_ns.class_('TemplateBinarySensor', binary_sensor.
 
 CONFIG_SCHEMA = binary_sensor.BINARY_SENSOR_SCHEMA.extend({
     cv.GenerateID(): cv.declare_id(TemplateBinarySensor),
-    cv.Optional(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_LAMBDA): cv.returning_lambda,
 }).extend(cv.COMPONENT_SCHEMA)
 
 
diff --git a/esphome/components/template/cover/__init__.py b/esphome/components/template/cover/__init__.py
index 0eccb9fc73..33b3b62870 100644
--- a/esphome/components/template/cover/__init__.py
+++ b/esphome/components/template/cover/__init__.py
@@ -18,7 +18,7 @@ RESTORE_MODES = {
 
 CONFIG_SCHEMA = cover.COVER_SCHEMA.extend({
     cv.GenerateID(): cv.declare_id(TemplateCover),
-    cv.Optional(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_LAMBDA): cv.returning_lambda,
     cv.Optional(CONF_OPTIMISTIC, default=False): cv.boolean,
     cv.Optional(CONF_ASSUMED_STATE, default=False): cv.boolean,
     cv.Optional(CONF_OPEN_ACTION): automation.validate_automation(single=True),
diff --git a/esphome/components/template/sensor/__init__.py b/esphome/components/template/sensor/__init__.py
index 788520877a..3fc71cf9de 100644
--- a/esphome/components/template/sensor/__init__.py
+++ b/esphome/components/template/sensor/__init__.py
@@ -9,7 +9,7 @@ TemplateSensor = template_ns.class_('TemplateSensor', sensor.Sensor, cg.PollingC
 
 CONFIG_SCHEMA = sensor.sensor_schema(UNIT_EMPTY, ICON_EMPTY, 1).extend({
     cv.GenerateID(): cv.declare_id(TemplateSensor),
-    cv.Optional(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_LAMBDA): cv.returning_lambda,
 }).extend(cv.polling_component_schema('60s'))
 
 
diff --git a/esphome/components/template/switch/__init__.py b/esphome/components/template/switch/__init__.py
index ac27770d47..783f5a1922 100644
--- a/esphome/components/template/switch/__init__.py
+++ b/esphome/components/template/switch/__init__.py
@@ -10,7 +10,7 @@ TemplateSwitch = template_ns.class_('TemplateSwitch', switch.Switch, cg.Componen
 
 CONFIG_SCHEMA = switch.SWITCH_SCHEMA.extend({
     cv.GenerateID(): cv.declare_id(TemplateSwitch),
-    cv.Optional(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_LAMBDA): cv.returning_lambda,
     cv.Optional(CONF_OPTIMISTIC, default=False): cv.boolean,
     cv.Optional(CONF_ASSUMED_STATE, default=False): cv.boolean,
     cv.Optional(CONF_TURN_OFF_ACTION): automation.validate_automation(single=True),
diff --git a/esphome/components/template/text_sensor/__init__.py b/esphome/components/template/text_sensor/__init__.py
index 23b71a3974..dae99dc9bc 100644
--- a/esphome/components/template/text_sensor/__init__.py
+++ b/esphome/components/template/text_sensor/__init__.py
@@ -11,7 +11,7 @@ TemplateTextSensor = template_ns.class_('TemplateTextSensor', text_sensor.TextSe
 
 CONFIG_SCHEMA = text_sensor.TEXT_SENSOR_SCHEMA.extend({
     cv.GenerateID(): cv.declare_id(TemplateTextSensor),
-    cv.Optional(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_LAMBDA): cv.returning_lambda,
 }).extend(cv.polling_component_schema('60s'))
 
 
diff --git a/esphome/config_validation.py b/esphome/config_validation.py
index 56fb260679..e591a5d951 100644
--- a/esphome/config_validation.py
+++ b/esphome/config_validation.py
@@ -333,7 +333,7 @@ def templatable(other_validators):
 
     def validator(value):
         if isinstance(value, Lambda):
-            return lambda_(value)
+            return returning_lambda(value)
         if isinstance(other_validators, dict):
             return schema(value)
         return schema(value)
@@ -974,6 +974,20 @@ def lambda_(value):
     return value
 
 
+def returning_lambda(value):
+    """Coerce this configuration option to a lambda.
+
+    Additionally, make sure the lambda returns something.
+    """
+    value = lambda_(value)
+    if u'return' not in value.value:
+        raise Invalid("Lambda doesn't contain a 'return' statement, but the lambda "
+                      "is expected to return a value. \n"
+                      "Please make sure the lambda contains at least one "
+                      "return statement.")
+    return value
+
+
 def dimensions(value):
     if isinstance(value, list):
         if len(value) != 2: