diff --git a/src/plugins/projectexplorer/projectmacro.cpp b/src/plugins/projectexplorer/projectmacro.cpp
index 63f69b6986fc61e4c31eabd763da9650bd0d7f0d..5d2824f01dbf1d4a578fbaa3c83b94cddb58ebff 100644
--- a/src/plugins/projectexplorer/projectmacro.cpp
+++ b/src/plugins/projectexplorer/projectmacro.cpp
@@ -38,7 +38,11 @@ bool Macro::isValid() const
 QByteArray Macro::toByteArray() const
 {
     switch (type) {
-        case MacroType::Define: return QByteArray("#define ") + key + ' ' + value;
+        case MacroType::Define: {
+            if (value.isEmpty())
+               return QByteArray("#define ") + key;
+            return QByteArray("#define ") + key + ' ' + value;
+        }
         case MacroType::Undefine: return QByteArray("#undef ") + key;
         case MacroType::Invalid: break;
     }