diff --git a/src/slic3r/GUI/3DScene.cpp b/src/slic3r/GUI/3DScene.cpp
index 2916d0177..8094cdde1 100644
--- a/src/slic3r/GUI/3DScene.cpp
+++ b/src/slic3r/GUI/3DScene.cpp
@@ -1142,7 +1142,7 @@ void GLVolumeCollection::export_toolpaths_to_obj(const char* filename) const
         Color color;
         ::memcpy((void*)color.data(), (const void*)volume->color, 4 * sizeof(float));
         fprintf(fp, "\n# material volume %d\n", volumes_count);
-        fprintf(fp, "usemtl material_%lld\n", 1 + std::distance(colors.begin(), colors.find(color)));
+        fprintf(fp, "usemtl material_%lld\n", (long long)(1 + std::distance(colors.begin(), colors.find(color))));
 
         int base_vertex_id = vertices_count + 1;
         int base_normal_id = normals_count + 1;
@@ -1242,8 +1242,8 @@ static void thick_lines_to_indexed_vertex_array(
         // calculate new XY normals
         Vec2d xy_right_normal = unscale(line.normal()).normalized();
 
-        int idx_a[4];
-        int idx_b[4];
+        int idx_a[4] = { 0, 0, 0, 0 }; // initialized to avoid warnings
+        int idx_b[4] = { 0, 0, 0, 0 }; // initialized to avoid warnings
         int idx_last = int(volume.vertices_and_normals_interleaved.size() / 6);
 
         bool bottom_z_different = bottom_z_prev != bottom_z;
diff --git a/src/slic3r/GUI/BedShapeDialog.cpp b/src/slic3r/GUI/BedShapeDialog.cpp
index a9be260bd..90fc0ff80 100644
--- a/src/slic3r/GUI/BedShapeDialog.cpp
+++ b/src/slic3r/GUI/BedShapeDialog.cpp
@@ -446,7 +446,7 @@ void BedShapePanel::update_shape()
 		auto twopi = 2 * PI;
         auto edges = 72;
         std::vector<Vec2d> points;
-        for (size_t i = 1; i <= edges; ++i) {
+        for (int i = 1; i <= edges; ++i) {
             auto angle = i * twopi / edges;
 			points.push_back(Vec2d(r*cos(angle), r*sin(angle)));
 		}
diff --git a/src/slic3r/GUI/GUI_Preview.cpp b/src/slic3r/GUI/GUI_Preview.cpp
index de6289f7d..6255c3934 100644
--- a/src/slic3r/GUI/GUI_Preview.cpp
+++ b/src/slic3r/GUI/GUI_Preview.cpp
@@ -680,7 +680,7 @@ void Preview::fill_slider_values(std::vector<std::pair<int, double>> &values,
                                  const std::vector<double> &layers_z)
 {
     values.clear();
-    for (int i = 0; i < layers_z.size(); ++i)
+    for (int i = 0; i < (int)layers_z.size(); ++i)
     {
         values.push_back(std::pair<int, double>(i + 1, layers_z[i]));
     }
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoScale.cpp b/src/slic3r/GUI/Gizmos/GLGizmoScale.cpp
index bf540cb00..a685fb774 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoScale.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoScale.cpp
@@ -329,6 +329,7 @@ void GLGizmoScale3D::do_scale_along_axis(Axis axis, const UpdateData& data)
             case X: { local_offset_vec = local_offset * Vec3d::UnitX(); break; }
             case Y: { local_offset_vec = local_offset * Vec3d::UnitY(); break; }
             case Z: { local_offset_vec = local_offset * Vec3d::UnitZ(); break; }
+            default: break;
             }
 
             m_offset = m_offsets_transform * local_offset_vec;
diff --git a/src/slic3r/GUI/Selection.cpp b/src/slic3r/GUI/Selection.cpp
index 9c1a84615..40fbbbac6 100644
--- a/src/slic3r/GUI/Selection.cpp
+++ b/src/slic3r/GUI/Selection.cpp
@@ -310,7 +310,7 @@ void Selection::remove_volume(unsigned int object_idx, unsigned int volume_idx)
     for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i)
     {
         GLVolume* v = (*m_volumes)[i];
-        if ((v->object_idx() == object_idx) && (v->volume_idx() == volume_idx))
+        if ((v->object_idx() == (int)object_idx) && (v->volume_idx() == (int)volume_idx))
             do_remove_volume(i);
     }
 
@@ -992,7 +992,7 @@ void Selection::translate(unsigned int object_idx, const Vec3d& displacement)
     for (unsigned int i : m_list)
     {
         GLVolume* v = (*m_volumes)[i];
-        if (v->object_idx() == object_idx)
+        if (v->object_idx() == (int)object_idx)
             v->set_instance_offset(v->get_instance_offset() + displacement);
     }
 
@@ -1037,7 +1037,7 @@ void Selection::translate(unsigned int object_idx, unsigned int instance_idx, co
     for (unsigned int i : m_list)
     {
         GLVolume* v = (*m_volumes)[i];
-        if ((v->object_idx() == object_idx) && (v->instance_idx() == instance_idx))
+        if ((v->object_idx() == (int)object_idx) && (v->instance_idx() == (int)instance_idx))
             v->set_instance_offset(v->get_instance_offset() + displacement);
     }
 
@@ -1063,7 +1063,7 @@ void Selection::translate(unsigned int object_idx, unsigned int instance_idx, co
                 continue;
 
             GLVolume* v = (*m_volumes)[j];
-            if ((v->object_idx() != object_idx) || (v->instance_idx() != instance_idx))
+            if ((v->object_idx() != object_idx) || (v->instance_idx() != (int)instance_idx))
                 continue;
 
             v->set_instance_offset(v->get_instance_offset() + displacement);
@@ -1154,7 +1154,7 @@ void Selection::erase()
         for (const ItemForDelete& i : items_set) {
             if (i.type == ItemType::itVolume) {
                 const int vol_in_obj_cnt = volumes_in_obj.find(i.obj_idx) == volumes_in_obj.end() ? 0 : volumes_in_obj.at(i.obj_idx);
-                if (vol_in_obj_cnt == m_model->objects[i.obj_idx]->volumes.size()) {
+                if (vol_in_obj_cnt == (int)m_model->objects[i.obj_idx]->volumes.size()) {
                     if (i.sub_obj_idx == vol_in_obj_cnt - 1)
                         items.emplace_back(ItemType::itObject, i.obj_idx, 0);
                     continue;
@@ -1389,7 +1389,7 @@ std::vector<unsigned int> Selection::get_volume_idxs_from_object(unsigned int ob
 
     for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i)
     {
-        if ((*m_volumes)[i]->object_idx() == object_idx)
+        if ((*m_volumes)[i]->object_idx() == (int)object_idx)
             idxs.push_back(i);
     }
 
@@ -1403,7 +1403,7 @@ std::vector<unsigned int> Selection::get_volume_idxs_from_instance(unsigned int
     for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i)
     {
         const GLVolume* v = (*m_volumes)[i];
-        if ((v->object_idx() == object_idx) && (v->instance_idx() == instance_idx))
+        if ((v->object_idx() == (int)object_idx) && (v->instance_idx() == (int)instance_idx))
             idxs.push_back(i);
     }
 
@@ -1417,9 +1417,9 @@ std::vector<unsigned int> Selection::get_volume_idxs_from_volume(unsigned int ob
     for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i)
     {
         const GLVolume* v = (*m_volumes)[i];
-        if ((v->object_idx() == object_idx) && (v->volume_idx() == volume_idx))
+        if ((v->object_idx() == (int)object_idx) && (v->volume_idx() == (int)volume_idx))
         {
-            if ((instance_idx != -1) && (v->instance_idx() == instance_idx))
+            if (((int)instance_idx != -1) && (v->instance_idx() == (int)instance_idx))
                 idxs.push_back(i);
         }
     }
@@ -1607,7 +1607,7 @@ void Selection::update_type()
             }
             else
             {
-                int sels_cntr = 0;
+                unsigned int sels_cntr = 0;
                 for (ObjectIdxsToInstanceIdxsMap::iterator it = m_cache.content.begin(); it != m_cache.content.end(); ++it)
                 {
                     const ModelObject* model_object = m_model->objects[it->first];
@@ -1759,7 +1759,7 @@ void Selection::do_remove_instance(unsigned int object_idx, unsigned int instanc
     for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i)
     {
         GLVolume* v = (*m_volumes)[i];
-        if ((v->object_idx() == object_idx) && (v->instance_idx() == instance_idx))
+        if ((v->object_idx() == (int)object_idx) && (v->instance_idx() == (int)instance_idx))
             do_remove_volume(i);
     }
 }
@@ -1769,7 +1769,7 @@ void Selection::do_remove_object(unsigned int object_idx)
     for (unsigned int i = 0; i < (unsigned int)m_volumes->size(); ++i)
     {
         GLVolume* v = (*m_volumes)[i];
-        if (v->object_idx() == object_idx)
+        if (v->object_idx() == (int)object_idx)
             do_remove_volume(i);
     }
 }
@@ -1836,7 +1836,6 @@ void Selection::render_synchronized_volumes() const
     {
         const GLVolume* volume = (*m_volumes)[i];
         int object_idx = volume->object_idx();
-        int instance_idx = volume->instance_idx();
         int volume_idx = volume->volume_idx();
         for (unsigned int j = 0; j < (unsigned int)m_volumes->size(); ++j)
         {