diff --git a/sshcr.h b/sshcr.h
index 18a31ff5..5abf4c17 100644
--- a/sshcr.h
+++ b/sshcr.h
@@ -46,9 +46,40 @@
         } while (0)
 #define crStop(z)       do{ *crLine = 0; return (z); }while(0)
 #define crStopV         do{ *crLine = 0; return; }while(0)
-#define crWaitUntil(c)  do { crReturn(0); } while (!(c))
-#define crWaitUntilV(c) do { crReturnV; } while (!(c))
-#define crMaybeWaitUntil(c) do { while (!(c)) crReturn(0); } while (0)
-#define crMaybeWaitUntilV(c) do { while (!(c)) crReturnV; } while (0)
+
+/*
+ * The crMaybeWaitUntil macros could have been more easily written in
+ * terms of the simple crReturn above, by writing things like
+ *
+ *       while (!condition) { crReturn(whatever); }
+ *
+ * (or do-while in the case of crWaitUntil). But it's better to do it
+ * directly by writing _once_ to crLine before first testing the
+ * condition, because this way it's robust against the condition check
+ * potentially freeing the entire coroutine state structure as a side
+ * effect (as long as it also evaluates false if it does that),
+ * because we don't write into crLine between the condition evaluating
+ * to false and the 'return' statement.
+ */
+#define crMaybeWaitUntil(c)                     \
+    do {                                        \
+        *crLine =__LINE__;                      \
+        case __LINE__: if (!(c)) return 0;      \
+    } while (0)
+#define crMaybeWaitUntilV(c)                    \
+    do {                                        \
+        *crLine =__LINE__;                      \
+        case __LINE__: if (!(c)) return;        \
+    } while (0)
+#define crWaitUntil(c)                          \
+    do {                                        \
+        *crLine =__LINE__; return;              \
+        case __LINE__: if (!(c)) return 0;      \
+    } while (0)
+#define crWaitUntilV(c)                         \
+    do {                                        \
+        *crLine =__LINE__; return;              \
+        case __LINE__: if (!(c)) return;        \
+    } while (0)
 
 #endif /* PUTTY_SSHCR_H */