diff --git a/src/lint.c b/src/lint.c
index b8d04901..14b1c4ad 100644
--- a/src/lint.c
+++ b/src/lint.c
@@ -684,6 +684,18 @@ static void check_dup_keys(ASTNode *node, LintContext *ctx) {
             for (int i = 0; i < node->data.list.count; i++)
                 check_dup_keys(node->data.list.elems[i], ctx);
             break;
+        case AST_MATCH:
+            check_dup_keys(node->data.match.expr, ctx);
+            for (int i = 0; i < node->data.match.case_count; i++) {
+                check_dup_keys(node->data.match.patterns[i], ctx);
+                for (int j = 0; j < node->data.match.body_counts[i]; j++)
+                    check_dup_keys(node->data.match.bodies[i][j], ctx);
+            }
+            break;
+        case AST_UNOBSERVED:
+            for (int i = 0; i < node->data.block.count; i++)
+                check_dup_keys(node->data.block.stmts[i], ctx);
+            break;
         /* Nothing to do for these. Enumerated rather than covered by a `default:`
          * so that -Werror=switch (Makefile CFLAGS) makes a new ASTType a build
          * error here instead of a silent no-op. */
@@ -704,9 +716,7 @@ static void check_dup_keys(ASTNode *node, LintContext *ctx) {
         case AST_CONTINUE:
         case AST_DOT_ASSIGN:
         case AST_IMPORT:
-        case AST_MATCH:
         case AST_LAMBDA:
-        case AST_UNOBSERVED:
         case AST_INDEX_ASSIGN:
         case AST_LIST_PATTERN_ASSIGN:
         case AST_SLICE:
diff --git a/tests/test_lint.sh b/tests/test_lint.sh
index 9b84ead2..dd238657 100644
--- a/tests/test_lint.sh
+++ b/tests/test_lint.sh
@@ -90,6 +90,63 @@ OUTPUT=$($EIGS --lint "$TMPFILE" 2>&1 || true)
 check_contains "duplicate dict key" "$OUTPUT" "duplicate dict key 'a'"
 rm -f "$TMPFILE"
 
+# --- #783: W010 (duplicate dict key) recurses into unobserved blocks ---
+# check_dup_keys used to break on AST_UNOBSERVED, so a dict literal inside
+# an unobserved: block was never reached and never warned on.
+TMPFILE=$(mktemp /tmp/lint_test_XXXXXX.eigs)
+cat > "$TMPFILE" << 'EIGS'
+unobserved:
+    w010_d is {"a": 1, "a": 2}
+print of w010_d
+EIGS
+OUTPUT=$($EIGS --lint "$TMPFILE" 2>&1 || true)
+check_contains "#783 W010 fires inside an unobserved block" "$OUTPUT" "W010.*'a'"
+rm -f "$TMPFILE"
+
+# --- #783: W010 (duplicate dict key) recurses into match arms ---
+# check_dup_keys used to break on AST_MATCH, so a dict literal inside a
+# match arm was never reached and never warned on.
+TMPFILE=$(mktemp /tmp/lint_test_XXXXXX.eigs)
+cat > "$TMPFILE" << 'EIGS'
+match 1:
+    case 1:
+        w010_d is {"a": 1, "a": 2}
+    case _:
+        x is 0
+print of 1
+EIGS
+OUTPUT=$($EIGS --lint "$TMPFILE" 2>&1 || true)
+check_contains "#783 W010 fires inside a match arm" "$OUTPUT" "W010.*'a'"
+rm -f "$TMPFILE"
+
+# --- #783: W010 (duplicate dict key) recurses into the match scrutinee ---
+TMPFILE=$(mktemp /tmp/lint_test_XXXXXX.eigs)
+cat > "$TMPFILE" << 'EIGS'
+match {"a": 1, "a": 2}:
+    case _:
+        print of "fallback"
+EIGS
+OUTPUT=$($EIGS --lint "$TMPFILE" 2>&1 || true)
+check_contains "#783 W010 fires in the match scrutinee" "$OUTPUT" "W010.*'a'"
+rm -f "$TMPFILE"
+
+# --- #783: W010 (duplicate dict key) recurses into match patterns ---
+# Patterns are full expressions (parser.c parses them with parse_expression),
+# so a dict literal used as a case pattern must be walked too. The wildcard
+# case _ stores a NULL pattern; check_dup_keys' !node guard covers it.
+TMPFILE=$(mktemp /tmp/lint_test_XXXXXX.eigs)
+cat > "$TMPFILE" << 'EIGS'
+x is 1
+match x:
+    case {"a": 1, "a": 2}:
+        print of "dict"
+    case _:
+        print of "other"
+EIGS
+OUTPUT=$($EIGS --lint "$TMPFILE" 2>&1 || true)
+check_contains "#783 W010 fires in a match pattern" "$OUTPUT" "W010.*'a'"
+rm -f "$TMPFILE"
+
 # --- Multiple warnings on one file ---
 TMPFILE=$(mktemp /tmp/lint_test_XXXXXX.eigs)
 cat > "$TMPFILE" << 'EIGS'