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	2023-10-17 14:50:53.000000000 +0200
+++ qtbase-everywhere-src-5.15.12-new/qmake/generators/makefile.cpp	2024-02-15 09:58:48.007291037 +0100
@@ -3242,7 +3242,7 @@ MakefileGenerator::openOutput(QFile &fil
 }
 
 QString
-MakefileGenerator::pkgConfigFileName(bool fixify)
+MakefileGenerator::pkgConfigFileName(bool fixify, bool onlyPrependDestdir)
 {
     QString ret = project->first("QMAKE_PKGCONFIG_FILE").toQString();
     if (ret.isEmpty()) {
@@ -3267,7 +3267,11 @@ MakefileGenerator::pkgConfigFileName(boo
     if(fixify) {
         if(QDir::isRelativePath(ret) && !project->isEmpty("DESTDIR"))
             ret.prepend(project->first("DESTDIR").toQString());
-        ret = fileFixify(ret, FileFixifyBackwards);
+        if (onlyPrependDestdir) {
+            ret = Option::fixPathToLocalOS(ret);
+        } else {
+            ret = fileFixify(ret, FileFixifyBackwards);
+        }
     }
     return ret;
 }
diff -rupN --no-dereference qtbase-everywhere-src-5.15.12/qmake/generators/makefile.h qtbase-everywhere-src-5.15.12-new/qmake/generators/makefile.h
--- qtbase-everywhere-src-5.15.12/qmake/generators/makefile.h	2023-10-17 14:50:53.000000000 +0200
+++ qtbase-everywhere-src-5.15.12-new/qmake/generators/makefile.h	2024-02-15 09:58:48.008291007 +0100
@@ -96,7 +96,7 @@ protected:
     virtual void writeDefaultVariables(QTextStream &t);
 
     QString pkgConfigPrefix() const;
-    QString pkgConfigFileName(bool fixify=true);
+    QString pkgConfigFileName(bool fixify=true, bool onlyPrependDestdir = false);
     QString pkgConfigFixPath(QString) const;
     void writePkgConfigFile();   // for pkg-config
 
diff -rupN --no-dereference qtbase-everywhere-src-5.15.12/qmake/generators/win32/winmakefile.cpp qtbase-everywhere-src-5.15.12-new/qmake/generators/win32/winmakefile.cpp
--- qtbase-everywhere-src-5.15.12/qmake/generators/win32/winmakefile.cpp	2024-02-15 09:58:39.949536122 +0100
+++ qtbase-everywhere-src-5.15.12-new/qmake/generators/win32/winmakefile.cpp	2024-02-15 09:58:48.011290918 +0100
@@ -782,7 +782,7 @@ QString Win32MakefileGenerator::defaultI
                 }
                 if(!ret.isEmpty())
                     ret += "\n\t";
-                ret += installMetaFile(ProKey("QMAKE_PKGCONFIG_INSTALL_REPLACE"), pkgConfigFileName(true), dst_pc);
+                ret += installMetaFile(ProKey("QMAKE_PKGCONFIG_INSTALL_REPLACE"), pkgConfigFileName(true, true), dst_pc);
                 if(!uninst.isEmpty())
                     uninst.append("\n\t");
                 uninst.append("-$(DEL_FILE) " + escapeFilePath(dst_pc));