diff --git a/src/asm/parser.y b/src/asm/parser.y
index c70cc927..4bcc7798 100644
--- a/src/asm/parser.y
+++ b/src/asm/parser.y
@@ -1026,15 +1026,16 @@ align_spec	: uconst {
 				$$.alignOfs = 0;
 			}
 		}
-		| uconst T_COMMA uconst {
+		| uconst T_COMMA const {
 			if ($1 > 16) {
 				error("Alignment must be between 0 and 16, not %u\n", $1);
-			} else if ($3 >= 1 << $1) {
-				error("Alignment offset (%u) must be smaller than alignment size (%u)\n",
-					$3, 1 << $1);
+			} else if ($3 <= -(1 << $1) || $3 >= 1 << $1) {
+				error("The absolute alignment offset (%" PRIu32
+				      ") must be less than alignment size (%d)\n",
+				      (uint32_t)($3 < 0 ? -$3 : $3), 1 << $1);
 			} else {
 				$$.alignment = $1;
-				$$.alignOfs = $3;
+				$$.alignOfs = $3 < 0 ? (1 << $1) + $3 : $3;
 			}
 		}
 ;
diff --git a/test/asm/align-large-ofs.err b/test/asm/align-large-ofs.err
index 611d1c81..1cbdb2fd 100644
--- a/test/asm/align-large-ofs.err
+++ b/test/asm/align-large-ofs.err
@@ -1,3 +1,3 @@
 error: align-large-ofs.asm(2):
-    Alignment offset (2) must be smaller than alignment size (2)
+    The absolute alignment offset (2) must be less than alignment size (2)
 error: Assembly aborted (1 error)!
diff --git a/test/asm/align-offset.asm b/test/asm/align-offset.asm
new file mode 100644
index 00000000..1d9d2343
--- /dev/null
+++ b/test/asm/align-offset.asm
@@ -0,0 +1,6 @@
+SECTION "good", ROM0, ALIGN[4, -2]
+align 4, 14 ; -2 == (1 << 4) - 2 == -2 mod (1 << 4)
+
+SECTION "bad+", ROM0, ALIGN[4, 18] ; out of range
+
+SECTION "bad-", ROM0, ALIGN[4, -20] ; out of range negative
diff --git a/test/asm/align-offset.err b/test/asm/align-offset.err
new file mode 100644
index 00000000..e3e3369a
--- /dev/null
+++ b/test/asm/align-offset.err
@@ -0,0 +1,5 @@
+error: align-offset.asm(4):
+    The absolute alignment offset (18) must be less than alignment size (16)
+error: align-offset.asm(6):
+    The absolute alignment offset (20) must be less than alignment size (16)
+error: Assembly aborted (2 errors)!