diff -up pkg-config-0.28/pkg.c.env pkg-config-0.28/pkg.c
--- pkg-config-0.28/pkg.c.env	2015-06-09 19:02:56.189243446 +0200
+++ pkg-config-0.28/pkg.c	2015-06-09 19:19:52.338657528 +0200
@@ -1012,6 +1012,24 @@ define_global_variable (const char *varn
 }
 
 char *
+var_to_env_var (const char *key, const char *var)
+{
+  char *new = g_strconcat ("PKG_CONFIG_", key, "_", var, NULL);
+  char *p;
+  for (p = new; *p != 0; p++)
+    {
+      char c = g_ascii_toupper (*p);
+
+      if (!g_ascii_isalnum (c))
+        c = '_';
+
+      *p = c;
+    }
+
+  return new;
+}
+
+char *
 package_get_var (Package *pkg,
                  const char *var)
 {
@@ -1019,7 +1037,17 @@ package_get_var (Package *pkg,
 
   if (globals)
     varval = g_strdup (g_hash_table_lookup (globals, var));
-  
+
+  if (pkg->key)
+    {
+      char *env_var = var_to_env_var (pkg->key, var);
+      const char *env_var_content = g_getenv (env_var);
+      g_free (env_var);
+      if (env_var_content)
+        return g_strdup (env_var_content);
+    }
+
+
   if (varval == NULL && pkg->vars)
     varval = g_strdup (g_hash_table_lookup (pkg->vars, var));