Index: config-kdevelop.h.cmake
===================================================================
--- config-kdevelop.h.cmake
+++ config-kdevelop.h.cmake
@@ -3,6 +3,8 @@
 
 /* config-kdevelop.h.  Generated by cmake from config-kdevelop.h.cmake */
 
+#define KDEVELOP_INSTALL_PREFIX "@CMAKE_INSTALL_PREFIX@"
+
 #cmakedefine01 KDEVELOP_SINGLE_APP
 
 #cmakedefine01 KF5SysGuard_FOUND
Index: plugins/cmake/cmakebuilddirchooser.ui
===================================================================
--- plugins/cmake/cmakebuilddirchooser.ui
+++ plugins/cmake/cmakebuilddirchooser.ui
@@ -79,6 +79,9 @@
        <verstretch>0</verstretch>
       </sizepolicy>
      </property>
+     <property name="toolTip">
+      <string>The prefix under which the project will be installed. Leaving this empty will let CMake use its default install prefix.</string>
+     </property>
     </widget>
    </item>
    <item row="4" column="0">
Index: plugins/cmake/cmakeutils.h
===================================================================
--- plugins/cmake/cmakeutils.h
+++ plugins/cmake/cmakeutils.h
@@ -116,7 +116,8 @@
     KDEVCMAKECOMMON_EXPORT KDevelop::Path currentCMakeExecutable(KDevelop::IProject* project, int builddir = -1);
 
     /**
-     * @returns the current install dir for the given project or "/usr/local" as default value.
+     * @returns the current install dir for the given project or an empty string if none has been defined
+     * (in that case, whatever default CMake sets for the platform will be used.)
      */
     KDEVCMAKECOMMON_EXPORT KDevelop::Path currentInstallDir( KDevelop::IProject* project, int builddir = -1 );
     
Index: plugins/cmake/cmakeutils.cpp
===================================================================
--- plugins/cmake/cmakeutils.cpp
+++ plugins/cmake/cmakeutils.cpp
@@ -359,13 +359,7 @@
 
 KDevelop::Path currentInstallDir( KDevelop::IProject* project, int builddir )
 {
-    const QString defaultInstallDir =
-#ifdef Q_OS_WIN
-        QStringLiteral("C:\\Program Files");
-#else
-        QStringLiteral("/usr/local");
-#endif
-    return KDevelop::Path(readBuildDirParameter( project, Config::Specific::cmakeInstallDirKey, defaultInstallDir, builddir ));
+    return KDevelop::Path(readBuildDirParameter( project, Config::Specific::cmakeInstallDirKey, QString(), builddir ));
 }
 
 QString projectRootRelative( KDevelop::IProject* project )
Index: plugins/manpage/manpageplugin.cpp
===================================================================
--- plugins/manpage/manpageplugin.cpp
+++ plugins/manpage/manpageplugin.cpp
@@ -18,6 +18,7 @@
     Boston, MA 02110-1301, USA.
 */
 
+#include "config-kdevelop.h"
 #include "manpageplugin.h"
 
 #include "manpagedocumentation.h"
@@ -93,7 +94,8 @@
 
     // Don't show man-page documentation for files that are not in /usr/include, because then we
     // most probably will be confusing the global function-name with a local one
-    if (!dec->topContext()->url().str().startsWith(QLatin1String("/usr/")))
+    if (!dec->topContext()->url().str().startsWith(QLatin1String("/usr/"))
+            && !dec->topContext()->url().str().startsWith(QLatin1String(KDEVELOP_INSTALL_PREFIX)))
         return {};
 
     ///@todo Do more verification to make sure that we're showing the correct documentation for the declaration