diff --git a/data/c++.m4 b/data/c++.m4
index 38a08328..fd5ec182 100644
--- a/data/c++.m4
+++ b/data/c++.m4
@@ -272,7 +272,7 @@ m4_define([b4_symbol_type_declare],
       location_type location;])[
 
     private:
-#if defined __cplusplus && __cplusplus < 201103L
+#if !defined __cplusplus || __cplusplus < 201103L
       /// Assignment operator.
       basic_symbol& operator= (const basic_symbol& other);
 #endif
diff --git a/data/lalr1.cc b/data/lalr1.cc
index f38015ba..30c6f7b9 100644
--- a/data/lalr1.cc
+++ b/data/lalr1.cc
@@ -335,7 +335,7 @@ m4_define([b4_shared_declarations],
       stack_symbol_type (YY_RVREF (stack_symbol_type) that);
       /// Steal the contents from \a sym to build this.
       stack_symbol_type (state_type s, YY_MOVE_REF (symbol_type) sym);
-#if defined __cplusplus && __cplusplus < 201103L
+#if !defined __cplusplus || __cplusplus < 201103L
       /// Assignment, needed by push_back by some old implementations.
       /// Moves the contents of that.
       stack_symbol_type& operator= (stack_symbol_type& that);
@@ -626,7 +626,7 @@ m4_if(b4_prefix, [yy], [],
     that.type = empty_symbol;
   }
 
-#if defined __cplusplus && __cplusplus < 201103L
+#if !defined __cplusplus || __cplusplus < 201103L
   ]b4_parser_class_name[::stack_symbol_type&
   ]b4_parser_class_name[::stack_symbol_type::operator= (stack_symbol_type& that)
   {
diff --git a/examples/c++/variant.yy b/examples/c++/variant.yy
index f77a746a..8fba6325 100644
--- a/examples/c++/variant.yy
+++ b/examples/c++/variant.yy
@@ -98,7 +98,7 @@ item:
 namespace yy
 {
   // Use nullptr with pre-C++11.
-#if defined __cplusplus && __cplusplus < 201103L
+#if !defined __cplusplus || __cplusplus < 201103L
 # define NULLPTR 0
 #else
 # define NULLPTR nullptr
diff --git a/tests/local.at b/tests/local.at
index 7ab7dbfc..89a117b8 100644
--- a/tests/local.at
+++ b/tests/local.at
@@ -912,14 +912,14 @@ m4_define([AT_REQUIRE_CXX_VERSION],
 [AT_DATA([check.cc],
 [[int main ()
 {
-#if __cplusplus < ]m4_case([$1],
-                           [98], [199711],
-                           [03], [199711],
-                           [11], [201103],
-                           [14], [201402],
-                           [17], [201703],
-                           [2a], [201709],
-                           [m4_fatal([$0: invalid arguments: $@])])[
+#if !defined __cplusplus || __cplusplus < ]m4_case([$1],
+    [98], [199711],
+    [03], [199711],
+    [11], [201103],
+    [14], [201402],
+    [17], [201703],
+    [2a], [201709],
+    [m4_fatal([$0: invalid arguments: $@])])[
   return 77;
 #else
   return 0;
diff --git a/tests/testsuite.h b/tests/testsuite.h
index e4c8298d..7e8e0599 100644
--- a/tests/testsuite.h
+++ b/tests/testsuite.h
@@ -7,7 +7,7 @@
 /* In C++ pre C++11 it is standard practice to use 0 for the null
    pointer.  But GCC -std=c++98 with -Wzero-as-null-pointer-constant
    warns about this.  Warning introduced in GCC 4.7. */
-#if defined __cplusplus && __cplusplus < 201103L
+#if !defined __cplusplus || __cplusplus < 201103L
 # if defined __GNUC__ && ! defined __clang__ && 407 <= __GNUC__ * 100 + __GNUC_MINOR__
 #  pragma GCC diagnostic ignored "-Wzero-as-null-pointer-constant"
 # endif