diff --git a/CMakeLists.txt b/CMakeLists.txt
index fb7f4ebd7e..d9f3322175 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -313,6 +313,10 @@ target_compile_options(geos_developer_cxx_flags
     $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>>:-Wno-unknown-warning-option>
     )
 
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 9.2)
+  target_compile_options(geos_developer_cxx_flags INTERFACE -Wsuggest-override)
+endif()
+
 #-----------------------------------------------------------------------------
 # Define a coverage build
 #-----------------------------------------------------------------------------
diff --git a/capi/geos_ts_c.cpp b/capi/geos_ts_c.cpp
index b6efb7e03e..ef238229aa 100644
--- a/capi/geos_ts_c.cpp
+++ b/capi/geos_ts_c.cpp
@@ -1629,13 +1629,13 @@ extern "C" {
     Geometry*
     GEOSGeom_transformXY_r(GEOSContextHandle_t handle, const GEOSGeometry* g, GEOSTransformXYCallback callback, void* userdata) {
 
-        struct TransformFilter : public geos::geom::CoordinateFilter {
+        struct TransformFilter final: public geos::geom::CoordinateFilter {
             TransformFilter(GEOSTransformXYCallback p_callback,
                             void* p_userdata) :
                             m_callback(p_callback),
                             m_userdata(p_userdata) {}
 
-            void filter_rw(CoordinateXY* c) const final {
+            void filter_rw(CoordinateXY* c) const override {
                 if (!m_callback(&(c->x), &(c->y), m_userdata)) {
                     throw std::runtime_error(std::string("Failed to transform coordinates."));
                 }
diff --git a/include/geos/algorithm/hull/HullTriangulation.h b/include/geos/algorithm/hull/HullTriangulation.h
index f6db2eac8d..05808c8425 100644
--- a/include/geos/algorithm/hull/HullTriangulation.h
+++ b/include/geos/algorithm/hull/HullTriangulation.h
@@ -124,7 +124,7 @@ class HullTriangulation
                 : triList(p_triList)
                 {};
 
-            void visit(std::array<QuadEdge*, 3>& triEdges);
+            void visit(std::array<QuadEdge*, 3>& triEdges) override;
 
     }; // HullTriVisitor
 
diff --git a/include/geos/precision/PointwisePrecisionReducerTransformer.h b/include/geos/precision/PointwisePrecisionReducerTransformer.h
index 1b5df1db42..9ea06717ff 100644
--- a/include/geos/precision/PointwisePrecisionReducerTransformer.h
+++ b/include/geos/precision/PointwisePrecisionReducerTransformer.h
@@ -63,7 +63,7 @@ class GEOS_DLL PointwisePrecisionReducerTransformer : public geom::util::Geometr
 
     std::unique_ptr<geom::CoordinateSequence> transformCoordinates(
         const geom::CoordinateSequence* coords,
-        const geom::Geometry* parent);
+        const geom::Geometry* parent) override;
 
 
 };
diff --git a/src/operation/overlayng/OverlayPoints.cpp b/src/operation/overlayng/OverlayPoints.cpp
index c1c37799cc..6afe7a2112 100644
--- a/src/operation/overlayng/OverlayPoints.cpp
+++ b/src/operation/overlayng/OverlayPoints.cpp
@@ -27,14 +27,14 @@ namespace geos {      // geos
 namespace operation { // geos.operation
 namespace overlayng { // geos.operation.overlayng
 
-struct PointExtractingFilter: public GeometryComponentFilter {
+struct PointExtractingFilter final: public GeometryComponentFilter {
 
     PointExtractingFilter(std::map<CoordinateXY, std::unique_ptr<Point>>& p_ptMap, const PrecisionModel* p_pm)
         : ptMap(p_ptMap), pm(p_pm)
     {}
 
     void
-    filter_ro(const Geometry* geom)
+    filter_ro(const Geometry* geom) override
     {
         if (geom->getGeometryTypeId() != GEOS_POINT) return;
 
diff --git a/util/geosop/GeosOp.cpp b/util/geosop/GeosOp.cpp
index 5774d7a77f..43a453b3ad 100644
--- a/util/geosop/GeosOp.cpp
+++ b/util/geosop/GeosOp.cpp
@@ -189,8 +189,8 @@ class comma_numpunct : public std::numpunct<char>
       :m_thousands_sep(p_thousands_sep),
        m_grouping(p_grouping){}
 protected:
-   char do_thousands_sep() const {return m_thousands_sep;}
-   std::string do_grouping() const {return m_grouping;}
+   char do_thousands_sep() const override {return m_thousands_sep;}
+   std::string do_grouping() const override {return m_grouping;}
 private:
    char m_thousands_sep;
    std::string m_grouping;