diff --git a/debian/changelog b/debian/changelog
index d644ec6..4ff113f 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -6,6 +6,7 @@ dump1090-mutability (1.08.2302.14+1mu-4) UNRELEASED; urgency=medium
   * Add support for controlling the accuracy of the receiver location
     written in the JSON metadata used by the webmap.
   * Oversampling is now less scary!
+  * Warn if --modeac is used together with --oversample.
 
  -- Oliver Jowett <oliver@mutability.co.uk>  Sat, 27 Dec 2014 20:08:44 +0000
 
diff --git a/dump1090.c b/dump1090.c
index f90c6f2..47f31f8 100644
--- a/dump1090.c
+++ b/dump1090.c
@@ -867,6 +867,12 @@ int main(int argc, char **argv) {
     if (Modes.interactive) {signal(SIGWINCH, sigWinchCallback);}
 #endif
 
+    if (Modes.mode_ac && Modes.oversample) {
+        fprintf(stderr,
+                "Warning: --modeac is currently ignored when --oversample is used;\n"
+                "         no ModeA/C messages will be decoded.\n");
+    }
+
     // Initialization
     modesInit();