diff --git a/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp b/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
--- a/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
+++ b/clang/lib/StaticAnalyzer/Core/RangeConstraintManager.cpp
@@ -600,9 +600,10 @@
   areEqual(ProgramStateRef State, SymbolRef First, SymbolRef Second);
 
   /// Iterate over all symbols and try to simplify them.
-  LLVM_NODISCARD ProgramStateRef simplify(SValBuilder &SVB,
-                                          RangeSet::Factory &F,
-                                          ProgramStateRef State);
+  LLVM_NODISCARD static inline ProgramStateRef simplify(SValBuilder &SVB,
+                                                        RangeSet::Factory &F,
+                                                        ProgramStateRef State,
+                                                        EquivalenceClass Class);
 
   void dumpToStream(ProgramStateRef State, raw_ostream &os) const;
   LLVM_DUMP_METHOD void dump(ProgramStateRef State) const {
@@ -1696,7 +1697,7 @@
   ClassMembersTy Members = State->get<ClassMembers>();
   for (std::pair<EquivalenceClass, SymbolSet> ClassToSymbolSet : Members) {
     EquivalenceClass Class = ClassToSymbolSet.first;
-    State = Class.simplify(Builder, RangeFactory, State);
+    State = EquivalenceClass::simplify(Builder, RangeFactory, State, Class);
     if (!State)
       return false;
     SimplifiedClasses.insert(Class);
@@ -1710,7 +1711,7 @@
     EquivalenceClass Class = ClassConstraint.first;
     if (SimplifiedClasses.count(Class)) // Already simplified.
       continue;
-    State = Class.simplify(Builder, RangeFactory, State);
+    State = EquivalenceClass::simplify(Builder, RangeFactory, State, Class);
     if (!State)
       return false;
   }
@@ -2090,18 +2091,17 @@
 // class to this class. This way, we simplify not just the symbols but the
 // classes as well: we strive to keep the number of the classes to be the
 // absolute minimum.
-LLVM_NODISCARD ProgramStateRef EquivalenceClass::simplify(
-    SValBuilder &SVB, RangeSet::Factory &F, ProgramStateRef State) {
-  SymbolSet ClassMembers = getClassMembers(State);
+LLVM_NODISCARD ProgramStateRef
+EquivalenceClass::simplify(SValBuilder &SVB, RangeSet::Factory &F,
+                           ProgramStateRef State, EquivalenceClass Class) {
+  SymbolSet ClassMembers = Class.getClassMembers(State);
   for (const SymbolRef &MemberSym : ClassMembers) {
     SymbolRef SimplifiedMemberSym = ento::simplify(State, MemberSym);
     if (SimplifiedMemberSym && MemberSym != SimplifiedMemberSym) {
-      EquivalenceClass ClassOfSimplifiedSym =
-          EquivalenceClass::find(State, SimplifiedMemberSym);
       // The simplified symbol should be the member of the original Class,
       // however, it might be in another existing class at the moment. We
       // have to merge these classes.
-      State = merge(F, State, ClassOfSimplifiedSym);
+      State = merge(F, State, MemberSym, SimplifiedMemberSym);
       if (!State)
         return nullptr;
     }
diff --git a/clang/test/Analysis/solver-sym-simplification-no-crash2.c b/clang/test/Analysis/solver-sym-simplification-no-crash2.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Analysis/solver-sym-simplification-no-crash2.c
@@ -0,0 +1,23 @@
+// RUN: %clang_analyze_cc1 %s \
+// RUN:   -analyzer-checker=core \
+// RUN:   -analyzer-checker=debug.ExprInspection \
+// RUN:   -verify
+
+// Here, we test that symbol simplification in the solver does not produce any
+// crashes.
+// https://bugs.llvm.org/show_bug.cgi?id=51109
+
+// expected-no-diagnostics
+
+int a, b, c, d;
+void f() {
+  a = -1;
+  d = b * a;
+  a = d / c;
+  if (a < 7 / b)
+    return;
+  if (d *a / c < 7 / b)
+    return;
+  if (b == 1 && c == -1)
+    return;
+}