diff --git a/pkg-r/R/TblSqlSource.R b/pkg-r/R/TblSqlSource.R
index 7ab55e7ac..847460ed3 100644
--- a/pkg-r/R/TblSqlSource.R
+++ b/pkg-r/R/TblSqlSource.R
@@ -171,10 +171,15 @@ TblSqlSource <- R6::R6Class(
         return(query)
       }
 
+      cte_body <- qualify_cte_table_refs(
+        private$conn,
+        as.character(private$tbl_cte)
+      )
+
       sprintf(
         "WITH %s AS (\n%s\n)\n%s",
         DBI::dbQuoteIdentifier(private$conn, self$table_name),
-        private$tbl_cte,
+        cte_body,
         query
       )
     },
@@ -196,3 +201,36 @@ TblSqlSource <- R6::R6Class(
     }
   )
 )
+
+# Get the current schema name for a DBI connection.
+# Tries `SELECT current_schema()` (DuckDB, PostgreSQL, etc.) and falls
+# back to "main" for databases that don't support it (SQLite).
+# @param conn A DBI connection
+# @return A character string with the schema name
+# @noRd
+get_current_schema <- function(conn) {
+  tryCatch(
+    DBI::dbGetQuery(conn, "SELECT current_schema()")[[1]],
+    error = function(e) "main"
+  )
+}
+
+# Schema-qualify table references in a CTE body to avoid circular
+# references. DuckDB 1.3.0+ and SQLite reject a CTE whose name matches
+# a table it references (e.g., `WITH t AS (SELECT ... FROM t) SELECT * FROM t`).
+# Prefixing the FROM/JOIN table with the schema name (e.g., `FROM main.t`)
+# disambiguates the CTE name from the physical table.
+# @param conn A DBI connection
+# @param cte_body A SQL string (the CTE body from dbplyr::remote_query())
+# @return The CTE body with table references schema-qualified
+# @noRd
+qualify_cte_table_refs <- function(conn, cte_body) {
+  schema <- as.character(DBI::dbQuoteIdentifier(conn, get_current_schema(conn)))
+
+  # Match FROM/JOIN followed by a table name (word or quoted identifier)
+  # that is not already schema-qualified (no dot immediately after).
+  # Subquery FROM clauses (FROM (SELECT ...)) are skipped because "(" is
+  # neither a word character nor a quoted identifier.
+  pattern <- "((?:FROM|JOIN)\\s+)([a-zA-Z_][a-zA-Z0-9_]*|\"[^\"]+\")(?![.])"
+  gsub(pattern, paste0("\\1", schema, ".\\2"), cte_body, perl = TRUE)
+}
diff --git a/pkg-r/tests/testthat/apps/basic/app.R b/pkg-r/tests/testthat/apps/basic/app.R
index efa2a9c7f..6a31f7463 100644
--- a/pkg-r/tests/testthat/apps/basic/app.R
+++ b/pkg-r/tests/testthat/apps/basic/app.R
@@ -24,12 +24,27 @@ dbDisconnect(conn)
 # Setup database source and QueryChat instance
 db_conn <- dbConnect(RSQLite::SQLite(), temp_db)
 
+# ellmer 0.5.0 moved model details out of `Provider` and into a new `Model`
+# class: `Provider()` no longer takes `model` as its second positional
+# argument, and `Chat$new()` now requires a separate `model` argument. `Model`
+# doesn't exist before 0.5.0, so branch on its presence to support both.
+mock_chat_client <- if (
+  exists("Model", where = asNamespace("ellmer"), inherits = FALSE)
+) {
+  MockChat$new(
+    ellmer::Provider("test", "test"),
+    model = ellmer::Model(name = "test")
+  )
+} else {
+  MockChat$new(ellmer::Provider("test", "test", "test"))
+}
+
 # Create QueryChat instance
 qc <- QueryChat$new(
   data_source = db_conn,
   table_name = "iris",
   greeting = "Welcome to the test app!",
-  client = MockChat$new(ellmer::Provider("test", "test", "test"))
+  client = mock_chat_client
 )
 
 ui <- page_sidebar(
diff --git a/pkg-r/tests/testthat/helper-fixtures.R b/pkg-r/tests/testthat/helper-fixtures.R
index 5180cf59d..7ce594ce5 100644
--- a/pkg-r/tests/testthat/helper-fixtures.R
+++ b/pkg-r/tests/testthat/helper-fixtures.R
@@ -173,7 +173,23 @@ mock_ellmer_chat_client <- function(
     private = private
   )
 
-  MockChat$new(ellmer::Provider("test", "test", "test"))
+  new_mock_chat(MockChat)
+}
+
+# ellmer 0.5.0 moved model details out of `Provider` and into a new `Model`
+# class: `Provider()` no longer takes `model` as its second positional
+# argument, and `Chat$new()` now requires a separate `model` argument. `Model`
+# doesn't exist before 0.5.0, so branch on its presence to support both.
+new_mock_chat <- function(MockChat, ...) {
+  if (exists("Model", where = asNamespace("ellmer"), inherits = FALSE)) {
+    MockChat$new(
+      ellmer::Provider("test", "test"),
+      model = ellmer::Model(name = "test"),
+      ...
+    )
+  } else {
+    MockChat$new(ellmer::Provider("test", "test", "test"), ...)
+  }
 }
 
 # shinychat::chat_restore() validates that `client` is an ellmer::Chat() R6