diff --git a/CHANGELOG.md b/CHANGELOG.md
index c2b3f59b8a..b44a798be6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -45,6 +45,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added Marius Staudt to list of reviewers [#1057](https://github.com/ie3-institute/simona/issues/1057)
 - Throw exception if the slack node is not directly conected to a transformer. [#525](https://github.com/ie3-institute/simona/issues/525)
 - Added support for topologies without transformers and slack grids with multiple nodes [#1099](https://github.com/ie3-institute/simona/issues/1099)
+- Checking the number of slack nodes [#1122](https://github.com/ie3-institute/simona/issues/1122)
 
 ### Changed
 - Adapted to changed data source in PSDM [#435](https://github.com/ie3-institute/simona/issues/435)
diff --git a/src/main/scala/edu/ie3/simona/io/grid/GridProvider.scala b/src/main/scala/edu/ie3/simona/io/grid/GridProvider.scala
index b4998c78a1..8777c1a3e9 100644
--- a/src/main/scala/edu/ie3/simona/io/grid/GridProvider.scala
+++ b/src/main/scala/edu/ie3/simona/io/grid/GridProvider.scala
@@ -7,6 +7,7 @@
 package edu.ie3.simona.io.grid
 
 import com.typesafe.scalalogging.LazyLogging
+import edu.ie3.datamodel.exceptions.InvalidGridException
 import edu.ie3.datamodel.io.naming.FileNamingStrategy
 import edu.ie3.datamodel.io.source.csv.{
   CsvJointGridContainerSource,
@@ -50,6 +51,22 @@ object GridProvider extends LazyLogging {
             // checks the grid container and throws exception if there is an error
             ValidationUtils.check(jointGridContainer)
 
+            // check number of slack nodes
+            val numberOfSlack =
+              jointGridContainer.getRawGrid.getNodes.asScala.filter(_.isSlack)
+
+            numberOfSlack.size match {
+              case 0 =>
+                throw new InvalidGridException(
+                  "The grid does not contain any slack node!"
+                )
+              case n if n > 1 =>
+                throw new InvalidGridException(
+                  s"The grid has $n slack nodes. This is currently not supported!"
+                )
+              case 1 =>
+            }
+
             jointGridContainer
           case None =>
             throw new RuntimeException(