https://bugs.gentoo.org/978404

--- a/common.mk   2026-07-03 17:07:42.176631332 +0300
+++ b/common.mk 2026-07-03 17:12:20.450178450 +0300
@@ -558,7 +558,7 @@
 # The following value, in a pkg-config file, sets the conventional pkg-config
 # variables that the pkg-config user can override at pkg-config time.
 PKGCONFIG_VAR_SET = \
-  prefix=$(PREFIX)\nexec_prefix=$${prefix}\nincludedir=$${prefix}/include\nlibdir=$${exec_prefix}/lib
+  prefix=$(PREFIX)\nexec_prefix=$${prefix}\nincludedir=$(HEADERINST_DIR)\nlibdir=$(LIBINST_DIR)
 
 
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