diff --git a/include/geos/operation/cluster/AbstractClusterFinder.h b/include/geos/operation/cluster/AbstractClusterFinder.h
index dfa5362480..0b66cd32e0 100644
--- a/include/geos/operation/cluster/AbstractClusterFinder.h
+++ b/include/geos/operation/cluster/AbstractClusterFinder.h
@@ -12,10 +12,8 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_ABSTRACTCLUSTERFINDER
-#define GEOS_OPERATION_CLUSTER_ABSTRACTCLUSTERFINDER
+#pragma once
 
-#include <functional>
 #include <memory>
 #include <vector>
 
@@ -132,5 +130,3 @@ class GEOS_DLL AbstractClusterFinder {
 }
 }
 }
-
-#endif
diff --git a/include/geos/operation/cluster/Clusters.h b/include/geos/operation/cluster/Clusters.h
index f4e49619cb..82f9d46c3b 100644
--- a/include/geos/operation/cluster/Clusters.h
+++ b/include/geos/operation/cluster/Clusters.h
@@ -12,8 +12,7 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_CLUSTERS
-#define GEOS_OPERATION_CLUSTER_CLUSTERS
+#pragma once
 
 #include <geos/export.h>
 #include <limits>
@@ -68,5 +67,3 @@ class GEOS_DLL Clusters {
 }
 }
 }
-
-#endif
diff --git a/include/geos/operation/cluster/DBSCANClusterFinder.h b/include/geos/operation/cluster/DBSCANClusterFinder.h
index dc63f3dfc5..be372010ef 100644
--- a/include/geos/operation/cluster/DBSCANClusterFinder.h
+++ b/include/geos/operation/cluster/DBSCANClusterFinder.h
@@ -12,8 +12,7 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_DBSCANCLUSTERFINDER
-#define GEOS_OPERATION_CLUSTER_DBSCANCLUSTERFINDER
+#pragma once
 
 #include <geos/operation/cluster/AbstractClusterFinder.h>
 #include <geos/geom/Geometry.h>
@@ -55,5 +54,3 @@ class GEOS_DLL DBSCANClusterFinder : public AbstractClusterFinder {
 }
 }
 }
-
-#endif
diff --git a/include/geos/operation/cluster/EnvelopeDistanceClusterFinder.h b/include/geos/operation/cluster/EnvelopeDistanceClusterFinder.h
index f847f0319d..eb7dfb25ae 100644
--- a/include/geos/operation/cluster/EnvelopeDistanceClusterFinder.h
+++ b/include/geos/operation/cluster/EnvelopeDistanceClusterFinder.h
@@ -12,8 +12,7 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_ENVELOPEDISTANCECLUSTERFINDER
-#define GEOS_OPERATION_CLUSTER_ENVELOPEDISTANCECLUSTERFINDER
+#pragma once
 
 #include <geos/operation/cluster/AbstractClusterFinder.h>
 #include <geos/geom/Envelope.h>
@@ -49,5 +48,3 @@ class GEOS_DLL EnvelopeDistanceClusterFinder : public AbstractClusterFinder {
 }
 }
 }
-
-#endif
diff --git a/include/geos/operation/cluster/EnvelopeIntersectsClusterFinder.h b/include/geos/operation/cluster/EnvelopeIntersectsClusterFinder.h
index 17bb0392de..4f2a7fd8c6 100644
--- a/include/geos/operation/cluster/EnvelopeIntersectsClusterFinder.h
+++ b/include/geos/operation/cluster/EnvelopeIntersectsClusterFinder.h
@@ -12,8 +12,7 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_ENVELOPEINTERSECTSCLUSTERFINDER
-#define GEOS_OPERATION_CLUSTER_ENVELOPEINTERSECTSCLUSTERFINDER
+#pragma once
 
 #include <geos/operation/cluster/AbstractClusterFinder.h>
 
@@ -40,5 +39,3 @@ class GEOS_DLL EnvelopeIntersectsClusterFinder : public AbstractClusterFinder {
 }
 }
 }
-
-#endif
\ No newline at end of file
diff --git a/include/geos/operation/cluster/GeometryDistanceClusterFinder.h b/include/geos/operation/cluster/GeometryDistanceClusterFinder.h
index 51645b6866..802b9b642b 100644
--- a/include/geos/operation/cluster/GeometryDistanceClusterFinder.h
+++ b/include/geos/operation/cluster/GeometryDistanceClusterFinder.h
@@ -12,8 +12,7 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_GEOMETRYDISTANCECLUSTERFINDER
-#define GEOS_OPERATION_CLUSTER_GEOMETRYDISTANCECLUSTERFINDER
+#pragma once
 
 #include <geos/operation/cluster/AbstractClusterFinder.h>
 #include <geos/geom/prep/PreparedGeometry.h>
@@ -55,5 +54,3 @@ class GEOS_DLL GeometryDistanceClusterFinder : public AbstractClusterFinder {
 }
 }
 }
-
-#endif
diff --git a/include/geos/operation/cluster/GeometryIntersectsClusterFinder.h b/include/geos/operation/cluster/GeometryIntersectsClusterFinder.h
index 8e4e1a17a7..8644e84508 100644
--- a/include/geos/operation/cluster/GeometryIntersectsClusterFinder.h
+++ b/include/geos/operation/cluster/GeometryIntersectsClusterFinder.h
@@ -12,8 +12,7 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_GEOMETRYINTERSECTSCLUSTERFINDER
-#define GEOS_OPERATION_CLUSTER_GEOMETRYINTERSECTSCLUSTERFINDER
+#pragma once
 
 #include <geos/operation/cluster/AbstractClusterFinder.h>
 #include <geos/geom/Geometry.h>
@@ -49,5 +48,3 @@ class GEOS_DLL GeometryIntersectsClusterFinder : public AbstractClusterFinder {
 }
 }
 }
-
-#endif
diff --git a/include/geos/operation/cluster/UnionFind.h b/include/geos/operation/cluster/UnionFind.h
index 2fe29e1ffd..af47151467 100644
--- a/include/geos/operation/cluster/UnionFind.h
+++ b/include/geos/operation/cluster/UnionFind.h
@@ -12,8 +12,7 @@
  *
  **********************************************************************/
 
-#ifndef GEOS_OPERATION_CLUSTER_UNIONFIND
-#define GEOS_OPERATION_CLUSTER_UNIONFIND
+#pragma once
 
 #include <algorithm>
 #include <numeric>
@@ -133,5 +132,3 @@ class GEOS_DLL UnionFind {
 }
 }
 }
-
-#endif