diff -rupN --no-dereference qtbase-everywhere-src-5.15.12/qmake/generators/makefile.cpp qtbase-everywhere-src-5.15.12-new/qmake/generators/makefile.cpp
--- qtbase-everywhere-src-5.15.12/qmake/generators/makefile.cpp	2024-02-15 09:58:49.325251777 +0100
+++ qtbase-everywhere-src-5.15.12-new/qmake/generators/makefile.cpp	2024-02-15 09:58:49.337251421 +0100
@@ -3256,6 +3256,9 @@ MakefileGenerator::pkgConfigFileName(boo
         if (dot != -1)
             ret = ret.left(dot);
     }
+    if (project->isActiveConfig("debug")) {
+        ret += "d";
+    }
     ret += Option::pkgcfg_ext;
     QString subdir = project->first("QMAKE_PKGCONFIG_DESTDIR").toQString();
     if(!subdir.isEmpty()) {