Index: clang/include/clang/Basic/DiagnosticParseKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticParseKinds.td
+++ clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -809,6 +809,8 @@
 def err_explicit_spec_non_template : Error<
   "explicit %select{specialization|instantiation}0 of "
   "%select{non-|undeclared }3template %1 %2">;
+def err_explicit_declaration_not_class : Error<
+  "'explicit' outside class declaration">;
 
 def err_default_template_template_parameter_not_template : Error<
   "default template argument for a template template parameter must be a class "
Index: clang/lib/Parse/ParseDecl.cpp
===================================================================
--- clang/lib/Parse/ParseDecl.cpp
+++ clang/lib/Parse/ParseDecl.cpp
@@ -3706,12 +3706,15 @@
       }
       break;
     case tok::kw_explicit: {
+      if (DSContext != DeclSpecContext::DSC_class) {
+        Diag(Tok.getLocation(), diag::err_explicit_declaration_not_class);
+      }
       SourceLocation ExplicitLoc = Loc;
       SourceLocation CloseParenLoc;
       ExplicitSpecifier ExplicitSpec(nullptr, ExplicitSpecKind::ResolvedTrue);
       ConsumedEnd = ExplicitLoc;
       ConsumeToken(); // kw_explicit
-      if (Tok.is(tok::l_paren)) {
+      if (Tok.is(tok::l_paren) && DSContext == DeclSpecContext::DSC_class) {
         if (getLangOpts().CPlusPlus20 || isExplicitBool() == TPResult::True) {
           Diag(Tok.getLocation(), getLangOpts().CPlusPlus20
                                       ? diag::warn_cxx17_compat_explicit_bool
Index: clang/test/Misc/explicit.c
===================================================================
--- /dev/null
+++ clang/test/Misc/explicit.c
@@ -0,0 +1,3 @@
+// Don't crash when explicit specifier is used outside of the class.
+int b = 0;
+int foo () { explicit ( && b );}