diff --git a/include/verilated_vpi.cpp b/include/verilated_vpi.cpp
index d8dd3ceb5..40192773d 100644
--- a/include/verilated_vpi.cpp
+++ b/include/verilated_vpi.cpp
@@ -173,20 +173,22 @@ class VerilatedVpioVarBase VL_NOT_FINAL : public VerilatedVpio {
 protected:
     const VerilatedVar* m_varp = nullptr;
     const VerilatedScope* m_scopep = nullptr;
-    std::string m_fullname;
+
+    // Usually empty, only gets filled when fullname() is called. Has to be stored as a member so
+    // the char* that fullname() returns is not a temporary.
+    mutable std::string m_fullname;
+
     int32_t m_indexedDim = -1;
     const VerilatedRange* get_range() const { return m_varp->range(m_indexedDim + 1); }
 
 public:
     VerilatedVpioVarBase(const VerilatedVar* varp, const VerilatedScope* scopep)
         : m_varp{varp}
-        , m_scopep{scopep}
-        , m_fullname{std::string{m_scopep->name()} + '.' + m_varp->name()} {}
+        , m_scopep{scopep} {}
     explicit VerilatedVpioVarBase(const VerilatedVpioVarBase* varp) {
         if (varp) {
             m_varp = varp->m_varp;
             m_scopep = varp->m_scopep;
-            m_fullname = varp->m_fullname;
             m_indexedDim = varp->m_indexedDim;
         }
     }
@@ -223,7 +225,10 @@ public:
     }
     const VerilatedRange* rangep() const override { return get_range(); }
     const char* name() const override { return m_varp->name(); }
-    const char* fullname() const override { return m_fullname.c_str(); }
+    const char* fullname() const override {
+        if (m_fullname.empty()) m_fullname = std::string{m_scopep->name()} + '.' + m_varp->name();
+        return m_fullname.c_str();
+    }
     virtual void* varDatap() const { return m_varp->datap(); }
     CData* varCDatap() const {
         VL_DEBUG_IFDEF(assert(varp()->vltype() == VLVT_UINT8););
@@ -2497,8 +2502,8 @@ void vpi_get_delays(vpiHandle /*object*/, p_vpi_delay /*delay_p*/) { VL_VPI_UNIM
 void vpi_put_delays(vpiHandle /*object*/, p_vpi_delay /*delay_p*/) { VL_VPI_UNIMP_(); }
 
 // value processing
-bool vl_check_format(const VerilatedVar* varp, const p_vpi_value valuep, const char* fullname,
-                     bool isGetValue) {
+bool vl_check_format(const VerilatedVpioVarBase* vop, const p_vpi_value valuep, bool isGetValue) {
+    const VerilatedVar* varp = vop->varp();
     bool status = true;
     if ((valuep->format == vpiVectorVal) || (valuep->format == vpiBinStrVal)
         || (valuep->format == vpiOctStrVal) || (valuep->format == vpiHexStrVal)) {
@@ -2555,7 +2560,7 @@ bool vl_check_format(const VerilatedVar* varp, const p_vpi_value valuep, const c
         status = false;
     }
     VL_VPI_ERROR_(__FILE__, __LINE__, "%s: Unsupported format (%s) for %s", __func__,
-                  VerilatedVpiError::strFromVpiVal(valuep->format), fullname);
+                  VerilatedVpiError::strFromVpiVal(valuep->format), vop->fullname());
     return status;
 }
 
@@ -2705,9 +2710,8 @@ void vl_vpi_put_word(const VerilatedVpioVar* vop, QData word, size_t bitCount, s
 void vl_vpi_get_value(const VerilatedVpioVarBase* vop, p_vpi_value valuep) {
     const VerilatedVar* const varp = vop->varp();
     void* const varDatap = vop->varDatap();
-    const char* fullname = vop->fullname();
 
-    if (!vl_check_format(varp, valuep, fullname, true)) return;
+    if (!vl_check_format(vop, valuep, true)) return;
     // string data type is dynamic and may vary in size during simulation
     static thread_local std::string t_outDynamicStr;
 
@@ -2894,7 +2898,7 @@ void vl_vpi_get_value(const VerilatedVpioVarBase* vop, p_vpi_value valuep) {
         return;
     }
     VL_VPI_ERROR_(__FILE__, __LINE__, "%s: Unsupported format (%s) as requested for %s", __func__,
-                  VerilatedVpiError::strFromVpiVal(valuep->format), fullname);
+                  VerilatedVpiError::strFromVpiVal(valuep->format), vop->fullname());
 }
 
 void vpi_get_value(vpiHandle object, p_vpi_value valuep) {
@@ -2955,8 +2959,7 @@ vpiHandle vpi_put_value(vpiHandle object, p_vpi_value valuep, p_vpi_time /*time_
                           baseSignalVop->fullname());
             return nullptr;
         }
-        if (!vl_check_format(baseSignalVop->varp(), valuep, baseSignalVop->fullname(), false))
-            return nullptr;
+        if (!vl_check_format(baseSignalVop, valuep, false)) return nullptr;
         if (delay_mode == vpiInertialDelay) {
             if (!VerilatedVpiPutHolder::canInertialDelay(valuep)) {
                 VL_VPI_WARNING_(