diff --git a/include/swift/Basic/LangOptions.h b/include/swift/Basic/LangOptions.h
index 58d3fdc8743..249a227bb7e 100644
--- a/include/swift/Basic/LangOptions.h
+++ b/include/swift/Basic/LangOptions.h
@@ -322,6 +322,9 @@ namespace swift {
     /// `@differentiable` declaration attribute, etc.
     bool EnableExperimentalDifferentiableProgramming = false;
 
+    /// Enable verification when every SubstitutionMap is constructed.
+    bool VerifyAllSubstitutionMaps = false;
+
     /// Sets the target we are building for and updates platform conditions
     /// to match.
     ///
@@ -512,6 +515,7 @@ namespace swift {
     /// Enable constraint solver support for experimental
     ///        operator protocol designator feature.
     bool SolverEnableOperatorDesignatedTypes = false;
+    
   };
 } // end namespace swift
 
diff --git a/include/swift/Option/FrontendOptions.td b/include/swift/Option/FrontendOptions.td
index b18dfb561dd..74c9385047e 100644
--- a/include/swift/Option/FrontendOptions.td
+++ b/include/swift/Option/FrontendOptions.td
@@ -548,6 +548,9 @@ def sil_merge_partial_modules : Flag<["-"], "sil-merge-partial-modules">,
 
 def sil_verify_all : Flag<["-"], "sil-verify-all">,
   HelpText<"Verify SIL after each transform">;
+  
+def verify_all_substitution_maps : Flag<["-"], "verify-all-substitution-maps">,
+  HelpText<"Verify all SubstitutionMaps on construction">;
 
 def sil_debug_serialization : Flag<["-"], "sil-debug-serialization">,
   HelpText<"Do not eliminate functions in Mandatory Inlining/SILCombine dead "
diff --git a/lib/AST/SubstitutionMap.cpp b/lib/AST/SubstitutionMap.cpp
index 0ecde91a8c4..026111141f8 100644
--- a/lib/AST/SubstitutionMap.cpp
+++ b/lib/AST/SubstitutionMap.cpp
@@ -56,7 +56,12 @@ SubstitutionMap::SubstitutionMap(
                                 GenericSignature genericSig,
                                 ArrayRef<Type> replacementTypes,
                                 ArrayRef<ProtocolConformanceRef> conformances)
-  : storage(Storage::get(genericSig, replacementTypes, conformances)) { }
+  : storage(Storage::get(genericSig, replacementTypes, conformances)) {
+#ifndef NDEBUG
+  if (genericSig->getASTContext().LangOpts.VerifyAllSubstitutionMaps)
+    verify();
+#endif
+}
 
 ArrayRef<Type> SubstitutionMap::getReplacementTypesBuffer() const {
   return storage ? storage->getReplacementTypes() : ArrayRef<Type>();
@@ -476,7 +481,7 @@ SubstitutionMap SubstitutionMap::subst(TypeSubstitutionFn subs,
       newConformances.push_back(
         conformance.subst(substType, subs, conformances, options));
     }
-
+    
     oldConformances = oldConformances.slice(1);
   }
 
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 3ea35141fb5..12db9b35232 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -565,6 +565,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                    Target.isOSDarwin());
   Opts.EnableSILOpaqueValues |= Args.hasArg(OPT_enable_sil_opaque_values);
 
+  Opts.VerifyAllSubstitutionMaps |= Args.hasArg(OPT_verify_all_substitution_maps);
+
   Opts.UseDarwinPreStableABIBit =
     (Target.isMacOSX() && Target.isMacOSXVersionLT(10, 14, 4)) ||
     (Target.isiOS() && Target.isOSVersionLT(12, 2)) ||
@@ -795,7 +797,7 @@ static bool ParseSearchPathArgs(SearchPathOptions &Opts,
   // Assumes exactly one of setMainExecutablePath() or setRuntimeIncludePath() 
   // is called before setTargetTriple() and parseArgs().
   // TODO: improve the handling of RuntimeIncludePath.
-
+  
   return false;
 }