diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2b47de59..8f9e99be 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## 0.17 - TBD
 
+Bug Fixes
+
+- Modified `binary-port?` and `textual-port?` to correctly differentiate between binary and textual ports.
+
 ## 0.16 - March 11, 2020
 
 Features
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 5860d234..e6e2bc1b 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -1100,6 +1100,8 @@ typedef struct {
   size_t str_bv_in_mem_buf_len;
 } port_type;
 
+#define CYC_BINARY_PORT_FLAG 0x10
+
 #define CYC_IO_BUF_LEN 1024
 
 /** Create a new port object in the nursery */
diff --git a/runtime.c b/runtime.c
index e2457b65..5c4e5ec7 100644
--- a/runtime.c
+++ b/runtime.c
@@ -4480,12 +4480,16 @@ port_type Cyc_io_open_output_file(void *data, object str)
 
 port_type Cyc_io_open_binary_input_file(void *data, object str)
 {
-  return _Cyc_io_open_input_file(data, str, "rb");
+  port_type p = _Cyc_io_open_input_file(data, str, "rb");
+  p.flags |= CYC_BINARY_PORT_FLAG;
+  return p;
 }
 
 port_type Cyc_io_open_binary_output_file(void *data, object str)
 {
-  return _Cyc_io_open_output_file(data, str, "wb");
+  port_type p = _Cyc_io_open_output_file(data, str, "wb");
+  p.flags |= CYC_BINARY_PORT_FLAG;
+  return p;
 }
 
 object Cyc_io_close_input_port(void *data, object port)
diff --git a/scheme/base.sld b/scheme/base.sld
index 6e297ef9..10ec40c9 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -694,12 +694,22 @@
                 (loop (if chr (cons chr acc) acc)
                       (- i 1)
                       (read-char port))))))))
-    ;; TODO: the following procedures should be a bit smarter, but we would
-    ;;       need to track binary/text as part of port_type
+    (define-c _binary-port?
+      "(void *data, int argc, closure _, object k, object obj)"
+      " object rv = boolean_f;
+        port_type *p = (port_type *)obj;
+        if (p->flags & CYC_BINARY_PORT_FLAG) {
+          rv = boolean_t;
+        }
+        return_closcall1(data, k, rv); ")
+
     (define (binary-port? obj)
-      (port? obj))
+      (and (port? obj)
+           (_binary-port? obj))
+      )
     (define (textual-port? obj)
-      (port? obj))
+      (and (port? obj)
+           (not (binary-port? obj))))
     ;;
     (define (flush-output-port . port)
       (if (null? port)