diff --git a/src/time/__tz.c b/src/time/__tz.c
index 3e2fcdcb..c34b3eb7 100644
--- a/src/time/__tz.c
+++ b/src/time/__tz.c
@@ -293,22 +293,20 @@ static size_t scan_trans(long long t, int local, size_t *alt)
 	n = (index-trans)>>scale;
 	if (a == n-1) return -1;
 	if (a == 0) {
-		x = zi_read32(trans + (a<<scale));
-		if (scale == 3) x = x<<32 | zi_read32(trans + (a<<scale) + 4);
+		x = zi_read32(trans);
+		if (scale == 3) x = x<<32 | zi_read32(trans + 4);
 		else x = (int32_t)x;
-		if (local) off = (int32_t)zi_read32(types + 6 * index[a-1]);
+		/* Find the lowest non-DST type, or 0 if none. */
+		size_t j = 0;
+		for (size_t i=abbrevs-types; i; i-=6) {
+			if (!types[i-6+4]) j = i-6;
+		}
+		if (local) off = (int32_t)zi_read32(types + j);
+		/* If t is before first transition, use the above-found type
+		 * and the index-zero (after transition) type as the alt. */
 		if (t - off < (int64_t)x) {
-			for (a=0; a<(abbrevs-types)/6; a++) {
-				if (types[6*a+4] != types[4]) break;
-			}
-			if (a == (abbrevs-types)/6) a = 0;
-			if (types[6*a+4]) {
-				*alt = a;
-				return 0;
-			} else {
-				*alt = 0;
-				return a;
-			}
+			if (alt) *alt = index[0];
+			return j/6;
 		}
 	}