diff --git a/etc/schema/dotnet-slnx.rnc b/etc/schema/dotnet-slnx.rnc
new file mode 100644
index 00000000000..2e081ed39fd
--- /dev/null
+++ b/etc/schema/dotnet-slnx.rnc
@@ -0,0 +1,74 @@
+default namespace = ""
+namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"
+namespace ns_1 = "http://relaxng.org/ns/compatibility/annotations/1.0"
+namespace rng = "http://relaxng.org/ns/structure/1.0"
+
+start |= starting_Solution
+starting_Solution =
+  element Solution {
+    (element Configurations { Configurations }?
+     | element Project { Project }*
+     | element Folder { Folder }*
+     | PropertiesGroup*)*,
+    attribute Description { xsd:string }?,
+    attribute Version { xsd:string }?
+  }
+Configurations =
+  (element BuildType {
+     attribute Name { xsd:string }
+   }*
+   | element Platform {
+       attribute Name { xsd:string }
+     }*
+   | element ProjectType { ProjectType }*)*
+ProjectType =
+  (ConfigurationRulesGroup*)*,
+  attribute TypeId { xsd:string }?,
+  attribute Name { xsd:string }?,
+  attribute Extension { xsd:string }?,
+  attribute BasedOn { xsd:string }?,
+  [ ns_1:defaultValue = "true" ] attribute IsBuildable { xsd:boolean }?,
+  [ ns_1:defaultValue = "true" ]
+  attribute SupportsPlatform { xsd:boolean }?
+Folder =
+  (element File {
+     attribute Path { xsd:string }
+   }*
+   | element Project { Project }*
+   | PropertiesGroup*)*,
+  attribute Name { xsd:string }
+Project =
+  (element BuildDependency {
+     attribute Project { text }
+   }*
+   | ConfigurationRulesGroup*
+   | PropertiesGroup*)*,
+  attribute Path { xsd:string },
+  attribute Type { xsd:string }?,
+  attribute DisplayName { xsd:string }?
+PropertiesGroup =
+  element Properties {
+    element Property {
+      attribute Name { xsd:string },
+      attribute Value { xsd:string }?
+    }*,
+    attribute Name { text },
+    attribute Scope { text }?
+  }
+ConfigurationRulesGroup =
+  element BuildType {
+    attribute Solution { xsd:string }?,
+    attribute Project { xsd:string }?
+  }+
+  | element Platform {
+      attribute Solution { xsd:string }?,
+      attribute Project { xsd:string }
+    }+
+  | element Build {
+      attribute Solution { xsd:string }?,
+      attribute Project { xsd:string }?
+    }+
+  | element Deploy {
+      attribute Solution { xsd:string }?,
+      attribute Project { xsd:string }?
+    }+
diff --git a/etc/schema/schemas.xml b/etc/schema/schemas.xml
index 18af8ccf4af..6701b9b56a6 100644
--- a/etc/schema/schemas.xml
+++ b/etc/schema/schemas.xml
@@ -93,4 +93,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>. -->
   <documentElement localName="Project" typeId="MSBuild"/>
   <typeId id="MSBuild" uri="msbuild.rnc" />
 
+  <uri pattern="*.slnx" typeId="Dotnet Slnx" />
+  <typeId id="Dotnet Slnx" uri="dotnet-slnx.rnc" />
+
 </locatingRules>
diff --git a/lisp/files.el b/lisp/files.el
index bd229673d8d..8cfbdc79bf0 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -3158,6 +3158,7 @@ ARC\\|ZIP\\|LZH\\|LHA\\|ZOO\\|[JEW]AR\\|XPI\\|RAR\\|CBR\\|7Z\\|SQUASHFS\\)\\'" .
     ("\\.oak\\'" . scheme-mode)
     ("\\.sgml?\\'" . sgml-mode)
     ("\\.x[ms]l\\'" . xml-mode)
+    ("\\.slnx\\'" . xml-mode)
     ("\\.dbk\\'" . xml-mode)
     ("\\.dtd\\'" . sgml-mode)
     ("\\.ds\\(ss\\)?l\\'" . dsssl-mode)