diff --git a/src/ModelingAlgorithms/TKBool/TopOpeBRep/TopOpeBRep_kpart.cxx b/src/ModelingAlgorithms/TKBool/TopOpeBRep/TopOpeBRep_kpart.cxx
index 94b16fbaa2..93c2eef937 100644
--- a/src/ModelingAlgorithms/TKBool/TopOpeBRep/TopOpeBRep_kpart.cxx
+++ b/src/ModelingAlgorithms/TKBool/TopOpeBRep/TopOpeBRep_kpart.cxx
@@ -38,7 +38,7 @@ extern bool TopOpeBRep_GetcontextNEWKP();
 
 // VP<STATIC_lastVPind> is the vp on which was computed the last CPI.
 // if no CPI is computed yet, <STATIC_lastVPind> = 0.
-static int STATIC_lastVPind;
+static thread_local int STATIC_lastVPind; // per-thread cross-call cache
 
 #define M_FORWARD(st) (st == TopAbs_FORWARD)
 #define M_REVERSED(st) (st == TopAbs_REVERSED)
diff --git a/src/ModelingAlgorithms/TKBool/TopOpeBRepBuild/TopOpeBRepBuild_Builder.cxx b/src/ModelingAlgorithms/TKBool/TopOpeBRepBuild/TopOpeBRepBuild_Builder.cxx
index d866d860a2..a8c5c95b2b 100644
--- a/src/ModelingAlgorithms/TKBool/TopOpeBRepBuild/TopOpeBRepBuild_Builder.cxx
+++ b/src/ModelingAlgorithms/TKBool/TopOpeBRepBuild/TopOpeBRepBuild_Builder.cxx
@@ -70,7 +70,8 @@ Standard_EXPORT void debspf(const int i)
 }
 #endif
 
-static int STATIC_SOLIDINDEX = 0;
+// Per-thread: a SplitSolid/FillSolid state flag; sharing it races concurrent builds.
+static thread_local int STATIC_SOLIDINDEX = 0;
 
 //=================================================================================================
 
diff --git a/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_ConstRad.cxx b/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_ConstRad.cxx
index 9b099dbcc9..08e0bb20a7 100644
--- a/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_ConstRad.cxx
+++ b/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_ConstRad.cxx
@@ -138,13 +138,12 @@ bool BlendFunc_ConstRad::ComputeValues(const math_Vector& X,
                                        const bool         byParam,
                                        const double       Param)
 {
-  // static declaration to avoid systematic reallocation
-
-  static gp_Vec d3u1, d3v1, d3uuv1, d3uvv1, d3u2, d3v2, d3uuv2, d3uvv2;
-  static gp_Vec d1gui, d2gui, d3gui;
-  static gp_Pnt ptgui;
-  static double invnormtg, dinvnormtg;
-  double        T = Param, aux;
+  // Per-thread scratch, reused across calls via the t_OK / myX_OK guards below.
+  static thread_local gp_Vec d3u1, d3v1, d3uuv1, d3uvv1, d3u2, d3v2, d3uuv2, d3uvv2;
+  static thread_local gp_Vec d1gui, d2gui, d3gui;
+  static thread_local gp_Pnt ptgui;
+  static thread_local double invnormtg, dinvnormtg;
+  double                     T = Param, aux;
 
   // Case of implicite parameter
   if (!byParam)
diff --git a/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_EvolRad.cxx b/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_EvolRad.cxx
index faf25679aa..a5b4d0df09 100644
--- a/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_EvolRad.cxx
+++ b/src/ModelingAlgorithms/TKFillet/BlendFunc/BlendFunc_EvolRad.cxx
@@ -196,13 +196,12 @@ bool BlendFunc_EvolRad::ComputeValues(const math_Vector& X,
                                       const bool         byParam,
                                       const double       Param)
 {
-  // static declaration to avoid systematic realloc
-
-  static gp_Vec d3u1, d3v1, d3uuv1, d3uvv1, d3u2, d3v2, d3uuv2, d3uvv2;
-  static gp_Vec d1gui, d2gui, d3gui;
-  static gp_Pnt ptgui;
-  static double invnormtg, dinvnormtg;
-  double        T = Param, aux;
+  // Per-thread scratch, reused across calls via the t_OK / myX_OK guards below.
+  static thread_local gp_Vec d3u1, d3v1, d3uuv1, d3uvv1, d3u2, d3v2, d3uuv2, d3uvv2;
+  static thread_local gp_Vec d1gui, d2gui, d3gui;
+  static thread_local gp_Pnt ptgui;
+  static thread_local double invnormtg, dinvnormtg;
+  double                     T = Param, aux;
 
   // Case of implicit parameter
   if (!byParam)
diff --git a/src/ModelingAlgorithms/TKFillet/ChFi3d/ChFi3d_Builder_6.cxx b/src/ModelingAlgorithms/TKFillet/ChFi3d/ChFi3d_Builder_6.cxx
index b4d23e9a8a..e1c8bb1d73 100644
--- a/src/ModelingAlgorithms/TKFillet/ChFi3d/ChFi3d_Builder_6.cxx
+++ b/src/ModelingAlgorithms/TKFillet/ChFi3d/ChFi3d_Builder_6.cxx
@@ -641,7 +641,8 @@ bool ChFi3d_Builder::StoreData(occ::handle<ChFiDS_SurfData>&         Data,
                                const bool                            Reversed)
 {
   // Small control tools.
-  static occ::handle<GeomAdaptor_Curve> checkcurve;
+  // Per-thread reused scratch adaptor.
+  static thread_local occ::handle<GeomAdaptor_Curve> checkcurve;
   if (checkcurve.IsNull())
   {
     checkcurve = new GeomAdaptor_Curve();