diff --git a/CHANGELOG.md b/CHANGELOG.md
index dff97050..6205faef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## 0.9.3 - TBD
 
+Bug Fixes
+
+- Fix `input-port?`, `output-port?`, `input-port-open?`, and `output-port-open?` to return `#f` instead of crashing when a non-port object is passed.
+
 ## 0.9.2 - August 26, 2018
 
 Features
diff --git a/scheme/base.sld b/scheme/base.sld
index 441d9785..3a9155c7 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -1360,7 +1360,9 @@
   (define-c input-port?
     "(void *data, int argc, closure _, object k, object port)"
     " port_type *p = (port_type *)port;
-      Cyc_check_port(data, port);
+      if (boolean_f == Cyc_is_port(port)) {
+        return_closcall1(data, k, boolean_f);
+      }
       return_closcall1(
         data, 
         k, 
@@ -1368,7 +1370,9 @@
   (define-c output-port?
     "(void *data, int argc, closure _, object k, object port)"
     " port_type *p = (port_type *)port;
-      Cyc_check_port(data, port);
+      if (boolean_f == Cyc_is_port(port)) {
+        return_closcall1(data, k, boolean_f);
+      }
       return_closcall1(
         data, 
         k, 
@@ -1376,7 +1380,9 @@
   (define-c input-port-open?
     "(void *data, int argc, closure _, object k, object port)"
     " port_type *p = (port_type *)port;
-      Cyc_check_port(data, port);
+      if (boolean_f == Cyc_is_port(port)) {
+        return_closcall1(data, k, boolean_f);
+      }
       return_closcall1(
         data, 
         k, 
@@ -1384,7 +1390,9 @@
   (define-c output-port-open?
     "(void *data, int argc, closure _, object k, object port)"
     " port_type *p = (port_type *)port;
-      Cyc_check_port(data, port);
+      if (boolean_f == Cyc_is_port(port)) {
+        return_closcall1(data, k, boolean_f);
+      }
       return_closcall1(
         data, 
         k,