diff --git a/src/V3DfgPeephole.cpp b/src/V3DfgPeephole.cpp
index af98ca8da..bb0fe31b8 100644
--- a/src/V3DfgPeephole.cpp
+++ b/src/V3DfgPeephole.cpp
@@ -1072,7 +1072,7 @@ class V3DfgPeephole final : public DfgVisitor {
     void visit(DfgArraySel* vtxp) override {
         if (DfgConst* const idxp = vtxp->bitp()->cast<DfgConst>()) {
             if (DfgVarArray* const varp = vtxp->fromp()->cast<DfgVarArray>()) {
-                const uint32_t idx = idxp->toU32();
+                const size_t idx = idxp->toSizeT();
                 if (DfgVertex* const driverp = varp->driverAt(idx)) {
                     APPLYING(INLINE_ARRAYSEL) {
                         vtxp->replaceWith(driverp);
@@ -1368,7 +1368,7 @@ class V3DfgPeephole final : public DfgVisitor {
                     return;
                 }
             }
-            if (vtxp->dtypep() == m_bitDType && rConstp->toU32() == 1) {
+            if (vtxp->dtypep() == m_bitDType && rConstp->hasValue(1)) {
                 APPLYING(REPLACE_SUB_WITH_NOT) {
                     DfgNot* const replacementp = new DfgNot{m_dfg, vtxp->fileline(), m_bitDType};
                     replacementp->srcp(lhsp);
@@ -1454,7 +1454,7 @@ class V3DfgPeephole final : public DfgVisitor {
             // 'cond ? a + 1 : a' -> 'a + cond'
             if (DfgAdd* const thenAddp = thenp->cast<DfgAdd>()) {
                 if (DfgConst* const constp = thenAddp->lhsp()->cast<DfgConst>()) {
-                    if (constp->toI32() == 1) {
+                    if (constp->hasValue(1)) {
                         if (thenAddp->rhsp() == elsep) {
                             APPLYING(REPLACE_COND_INC) {
                                 DfgConcat* const extp = new DfgConcat{m_dfg, flp, vtxp->dtypep()};
@@ -1474,7 +1474,7 @@ class V3DfgPeephole final : public DfgVisitor {
             // 'cond ? a - 1 : a' -> 'a - cond'
             if (DfgSub* const thenSubp = thenp->cast<DfgSub>()) {
                 if (DfgConst* const constp = thenSubp->rhsp()->cast<DfgConst>()) {
-                    if (constp->toI32() == 1) {
+                    if (constp->hasValue(1)) {
                         if (thenSubp->lhsp() == elsep) {
                             APPLYING(REPLACE_COND_DEC) {
                                 DfgConcat* const extp = new DfgConcat{m_dfg, flp, vtxp->dtypep()};
diff --git a/src/V3DfgVertices.h b/src/V3DfgVertices.h
index 8b003ace0..5c3700308 100644
--- a/src/V3DfgVertices.h
+++ b/src/V3DfgVertices.h
@@ -108,12 +108,21 @@ public:
     V3Number& num() { return m_num; }
     const V3Number& num() const { return m_num; }
 
-    uint32_t toU32() const { return num().toUInt(); }
-    int32_t toI32() const { return num().toSInt(); }
+    size_t toSizeT() const {
+        if VL_CONSTEXPR_CXX17 (sizeof(size_t) > sizeof(uint32_t)) {
+            return static_cast<size_t>(num().toUQuad());
+        }
+        return static_cast<size_t>(num().toUInt());
+    }
 
     bool isZero() const { return num().isEqZero(); }
     bool isOnes() const { return num().isEqAllOnes(width()); }
 
+    // Does this DfgConst have the given value? Note this is not easy to answer if wider than 32.
+    bool hasValue(uint32_t value) const {
+        return !num().isFourState() && num().edataWord(0) == value && num().mostSetBitP1() <= 32;
+    }
+
     std::pair<DfgEdge*, size_t> sourceEdges() override { return {nullptr, 0}; }
     std::pair<const DfgEdge*, size_t> sourceEdges() const override { return {nullptr, 0}; }
     const string srcName(size_t) const override {  // LCOV_EXCL_START
diff --git a/test_regress/t/t_dfg_peephole.v b/test_regress/t/t_dfg_peephole.v
index 675fd9194..e3e3862bd 100644
--- a/test_regress/t/t_dfg_peephole.v
+++ b/test_regress/t/t_dfg_peephole.v
@@ -175,6 +175,8 @@ module t (
    `signal(REMOVE_XOR_WITH_ONES, -64'd1 ^ rand_a);
    `signal(REPLACE_COND_DEC, randbit_a ? rand_b - 64'b1 : rand_b);
    `signal(REPLACE_COND_INC, randbit_a ? rand_b + 64'b1 : rand_b);
+   `signal(NO_REPLACE_COND_DEC, randbit_a ? rand_b - 64'hf000000000000000 : rand_b);
+   `signal(NO_REPLACE_COND_INC, randbit_a ? rand_b + 64'hf000000000000000 : rand_b);
    `signal(RIGHT_LEANING_ASSOC, (((rand_a + rand_b) + rand_a) + rand_b));
    `signal(RIGHT_LEANING_CONCET, {{{rand_a, rand_b}, rand_a}, rand_b});