diff --git a/src/libslic3r/Layer.cpp b/src/libslic3r/Layer.cpp
index 5c661ed68..f99cc674d 100644
--- a/src/libslic3r/Layer.cpp
+++ b/src/libslic3r/Layer.cpp
@@ -92,6 +92,25 @@ void Layer::restore_untyped_slices()
     }
 }
 
+// Similar to Layer::restore_untyped_slices()
+// To improve robustness of detect_surfaces_type() when reslicing (working with typed slices), see GH issue #7442.
+// Only resetting layerm->slices if Slice::extra_perimeters is always zero or it will not be used anymore
+// after the perimeter generator.
+void Layer::restore_untyped_slices_no_extra_perimeters()
+{
+    if (layer_needs_raw_backup(this)) {
+        for (LayerRegion *layerm : m_regions)
+        	if (layerm->region().config().extra_perimeters.value <= 0)
+            	layerm->slices.set(layerm->raw_slices, stInternal);
+    } else {
+    	assert(m_regions.size() == 1);
+    	LayerRegion *layerm = m_regions.front();
+    	// This optimization is correct, as extra_perimeters are only reused by prepare_infill() with multi-regions.
+        //if (layerm->region().config().extra_perimeters.value <= 0)
+        	layerm->slices.set(this->lslices, stInternal);
+    }
+}
+
 ExPolygons Layer::merged(float offset_scaled) const
 {
 	assert(offset_scaled >= 0.f);
@@ -179,7 +198,7 @@ void Layer::make_perimeters()
 	                // group slices (surfaces) according to number of extra perimeters
 	                std::map<unsigned short, Surfaces> slices;  // extra_perimeters => [ surface, surface... ]
 	                for (LayerRegion *layerm : layerms) {
-	                    for (Surface &surface : layerm->slices.surfaces)
+	                    for (const Surface &surface : layerm->slices.surfaces)
 	                        slices[surface.extra_perimeters].emplace_back(surface);
 	                    if (layerm->region().config().fill_density > layerm_config->region().config().fill_density)
 	                    	layerm_config = layerm;
diff --git a/src/libslic3r/Layer.hpp b/src/libslic3r/Layer.hpp
index 516b6da9b..0071c7f6e 100644
--- a/src/libslic3r/Layer.hpp
+++ b/src/libslic3r/Layer.hpp
@@ -137,6 +137,8 @@ public:
     //FIXME Review whether not to simplify the code by keeping the raw_slices all the time.
     void                    backup_untyped_slices();
     void                    restore_untyped_slices();
+    // To improve robustness of detect_surfaces_type() when reslicing (working with typed slices), see GH issue #7442.
+    void                    restore_untyped_slices_no_extra_perimeters();
     // Slices merged into islands, to be used by the elephant foot compensation to trim the individual surfaces with the shrunk merged slices.
     ExPolygons              merged(float offset) const;
     template <class T> bool any_internal_region_slice_contains(const T &item) const {
diff --git a/src/libslic3r/LayerRegion.cpp b/src/libslic3r/LayerRegion.cpp
index 4dbffe7b0..fd29d6d54 100644
--- a/src/libslic3r/LayerRegion.cpp
+++ b/src/libslic3r/LayerRegion.cpp
@@ -51,8 +51,7 @@ void LayerRegion::slices_to_fill_surfaces_clipped()
     // so we're safe. This guarantees idempotence of prepare_infill() also in case
     // that combine_infill() turns some fill_surface into VOID surfaces.
     // Collect polygons per surface type.
-    std::vector<SurfacesPtr> by_surface;
-    by_surface.assign(size_t(stCount), SurfacesPtr());
+    std::array<SurfacesPtr, size_t(stCount)> by_surface;
     for (Surface &surface : this->slices.surfaces)
         by_surface[size_t(surface.surface_type)].emplace_back(&surface);
     // Trim surfaces by the fill_boundaries.
diff --git a/src/libslic3r/PrintObject.cpp b/src/libslic3r/PrintObject.cpp
index 97d13af75..05b8c9eb6 100644
--- a/src/libslic3r/PrintObject.cpp
+++ b/src/libslic3r/PrintObject.cpp
@@ -227,6 +227,17 @@ void PrintObject::prepare_infill()
 
     m_print->set_status(30, L("Preparing infill"));
 
+    if (m_typed_slices) {
+        // To improve robustness of detect_surfaces_type() when reslicing (working with typed slices), see GH issue #7442.
+        // The preceding step (perimeter generator) only modifies extra_perimeters and the extra perimeters are only used by discover_vertical_shells()
+        // with more than a single region. If this step does not use Surface::extra_perimeters or Surface::extra_perimeters is always zero, it is safe
+        // to reset to the untyped slices before re-runnning detect_surfaces_type().
+        for (Layer* layer : m_layers) {
+            layer->restore_untyped_slices_no_extra_perimeters();
+            m_print->throw_if_canceled();
+        }
+    }
+
     // This will assign a type (top/bottom/internal) to $layerm->slices.
     // Then the classifcation of $layerm->slices is transfered onto 
     // the $layerm->fill_surfaces by clipping $layerm->fill_surfaces