https://github.com/mate-desktop/engrampa/commit/499e600d758578eeb8187f92d0c12b36e50f7595

--- a/src/fr-init.c
+++ b/src/fr-init.c
@@ -62,7 +62,8 @@
 	{ "application/x-7z-compressed-tar",    ".tar.7z",   N_("Tar compressed with 7z (.tar.7z)"), 0 },
 	{ "application/x-ace",                  ".ace",      N_("Ace (.ace)"), 0 },
 	{ "application/x-alz",                  ".alz",      NULL, 0 },
-	{ "application/x-ar",                   ".ar",       N_("Ar (.ar)"), 0 },
+	{ "application/x-ar",                   ".a",        N_("Ar (.a)"), 0 },
+  { "application/x-ar",                   ".ar",       N_("Ar (.ar)"), 0 },
 	{ "application/x-arj",                  ".arj",      N_("Arj (.arj)"), 0 },
 	{ "application/x-bzip",                 ".bz2",      NULL, 0 },
 	{ "application/x-bzip-compressed-tar",  ".tar.bz2",  N_("Tar compressed with bzip2 (.tar.bz2)"), 0 },
@@ -108,7 +109,8 @@
 	{ ".7z", "application/x-7z-compressed" },
 	{ ".ace", "application/x-ace" },
 	{ ".alz", "application/x-alz" },
-	{ ".ar", "application/x-ar" },
+	{ ".a", "application/x-ar" },
+  { ".ar", "application/x-ar" },
 	{ ".arj", "application/x-arj" },
 	{ ".bin", "application/x-stuffit" },
 	{ ".bz", "application/x-bzip" },