diff --git a/sqlalchemy_firebird/base.py b/sqlalchemy_firebird/base.py
index f74399e..a9ba973 100644
--- a/sqlalchemy_firebird/base.py
+++ b/sqlalchemy_firebird/base.py
@@ -3,7 +3,7 @@
 
 from packaging import version
 
-from typing import List
+from typing import Any, List
 from typing import Optional
 
 from sqlalchemy import __version__ as SQLALCHEMY_VERSION
@@ -377,19 +377,18 @@ def visit_boolean(self, type_, **kw):
     def visit_datetime(self, type_, **kw):
         return self.visit_TIMESTAMP(type_, **kw)
 
-    def _render_string_type(self, type_, name, length_override=None):
+    def _render_firebird_string_type(
+        self,
+        name: str,
+        length: Optional[int],
+        collation: Optional[str],
+        charset: Optional[str],
+    ) -> str:
         firebird_3_or_lower = (
             self.dialect.server_version_info
             and self.dialect.server_version_info < (4,)
         )
 
-        length = coalesce(
-            length_override,
-            getattr(type_, "length", None),
-        )
-        charset = getattr(type_, "charset", None)
-        collation = getattr(type_, "collation", None)
-
         if name in ["BINARY", "VARBINARY", "NCHAR", "NVARCHAR"]:
             charset = None
             collation = None
@@ -432,11 +431,33 @@ def _render_string_type(self, type_, name, length_override=None):
 
         return text
 
-    def visit_BINARY(self, type_, **kw):
-        return self._render_string_type(type_, "BINARY")
+    def visit_CHAR(self, type_: fb_types.FBCHAR, **kw: Any) -> str:
+        return self._render_firebird_string_type(
+            "CHAR",
+            type_.length,
+            type_.collation,
+            getattr(type_, "charset", None),
+        )
+
+    def visit_NCHAR(self, type_: fb_types.FBNCHAR, **kw: Any) -> str:
+        return self._render_firebird_string_type("NCHAR", type_.length, type_.collation)
 
-    def visit_VARBINARY(self, type_, **kw):
-        return self._render_string_type(type_, "VARBINARY")
+    def visit_VARCHAR(self, type_: fb_types.FBVARCHAR, **kw: Any) -> str:
+        return self._render_firebird_string_type(
+            "VARCHAR",
+            type_.length,
+            type_.collation,
+            getattr(type_, "charset", None),
+        )
+    
+    def visit_NVARCHAR(self, type_: fb_types.FBNCHAR, **kw: Any) -> str:
+        return self._render_firebird_string_type("NVARCHAR", type_.length, type_.collation)
+
+    def visit_BINARY(self, type_: fb_types.FBBINARY, **kw) -> str:
+        return self._render_firebird_string_type("BINARY", type_.length)
+
+    def visit_VARBINARY(self, type_: fb_types.FBVARBINARY, **kw) -> str:
+        return self._render_firebird_string_type("VARBINARY", type_.length)
 
     def visit_TEXT(self, type_, **kw):
         return self.visit_BLOB(type_, override_subtype=1, **kw)
@@ -490,9 +511,11 @@ def visit_TIMESTAMP(self, type_, **kw):
             return super().visit_TIMESTAMP(type_, **kw)
 
         return "TIMESTAMP%s %s" % (
-            "(%d)" % type_.precision
-            if getattr(type_, "precision", None) is not None
-            else "",
+            (
+                "(%d)" % type_.precision
+                if getattr(type_, "precision", None) is not None
+                else ""
+            ),
             (type_.timezone and "WITH" or "WITHOUT") + " TIME ZONE",
         )
 
@@ -501,9 +524,11 @@ def visit_TIME(self, type_, **kw):
             return super().visit_TIME(type_, **kw)
 
         return "TIME%s %s" % (
-            "(%d)" % type_.precision
-            if getattr(type_, "precision", None) is not None
-            else "",
+            (
+                "(%d)" % type_.precision
+                if getattr(type_, "precision", None) is not None
+                else ""
+            ),
             (type_.timezone and "WITH" or "WITHOUT") + " TIME ZONE",
         )