diff --git a/changes/ticket30519 b/changes/ticket30519
new file mode 100644
index 0000000000..efb25b9294
--- /dev/null
+++ b/changes/ticket30519
@@ -0,0 +1,4 @@
+  o Minor features (testing):
+    - When running tests in coverage mode, take additional care to make
+      our coverage deterministic, so that we can accurately track changes in
+      code coverage. Closes ticket 30519.
diff --git a/scripts/test/cov-test-determinism.sh b/scripts/test/cov-test-determinism.sh
index 3b4f372e04..3458f96968 100755
--- a/scripts/test/cov-test-determinism.sh
+++ b/scripts/test/cov-test-determinism.sh
@@ -25,6 +25,9 @@ else
 fi
 
 if test "$run" = 1; then
+    # same seed as in travis.yml
+    TOR_TEST_RNG_SEED="636f766572616765"
+    export TOR_TEST_RNG_SEED
     while true; do
         make reset-gcov
         CD=coverage-raw/coverage-$(date +%s)
diff --git a/src/lib/log/log.h b/src/lib/log/log.h
index a381220af0..4a3ea0ad55 100644
--- a/src/lib/log/log.h
+++ b/src/lib/log/log.h
@@ -194,6 +194,11 @@ void tor_log_get_logfile_names(struct smartlist_t *out);
 
 extern int log_global_min_severity_;
 
+#ifdef TOR_COVERAGE
+/* For coverage builds, we try to avoid our log_debug optimization, since it
+ * can have weird effects on internal macro coverage. */
+#define debug_logging_enabled() (1)
+#else
 static inline bool debug_logging_enabled(void);
 /**
  * Return true iff debug logging is enabled for at least one domain.
@@ -202,6 +207,7 @@ static inline bool debug_logging_enabled(void)
 {
   return PREDICT_UNLIKELY(log_global_min_severity_ == LOG_DEBUG);
 }
+#endif
 
 void log_fn_(int severity, log_domain_mask_t domain,
              const char *funcname, const char *format, ...)
diff --git a/src/lib/wallclock/timeval.h b/src/lib/wallclock/timeval.h
index 4967e939bf..33076adc8b 100644
--- a/src/lib/wallclock/timeval.h
+++ b/src/lib/wallclock/timeval.h
@@ -20,6 +20,27 @@
 #include <sys/time.h>
 #endif
 
+#ifdef TOR_COVERAGE
+/* For coverage builds, we use a slower definition of these macros without
+ * branches, to make coverage consistent. */
+#undef timeradd
+#undef timersub
+#define timeradd(tv1,tv2,tvout) \
+  do {                          \
+    (tvout)->tv_sec = (tv1)->tv_sec + (tv2)->tv_sec;    \
+    (tvout)->tv_usec = (tv1)->tv_usec + (tv2)->tv_usec; \
+    (tvout)->tv_sec += (tvout)->tv_usec / 1000000;      \
+    (tvout)->tv_usec %= 1000000;                        \
+  } while (0)
+#define timersub(tv1,tv2,tvout) \
+  do {                          \
+    (tvout)->tv_sec = (tv1)->tv_sec - (tv2)->tv_sec - 1;            \
+    (tvout)->tv_usec = (tv1)->tv_usec - (tv2)->tv_usec + 1000000;   \
+    (tvout)->tv_sec += (tvout)->tv_usec / 1000000;                  \
+    (tvout)->tv_usec %= 1000000;                                    \
+  } while (0)
+#endif
+
 #ifndef timeradd
 /** Replacement for timeradd on platforms that do not have it: sets tvout to
  * the sum of tv1 and tv2. */
diff --git a/src/test/include.am b/src/test/include.am
index 824089bc47..85f9c9f880 100644
--- a/src/test/include.am
+++ b/src/test/include.am
@@ -32,8 +32,15 @@ endif
 
 if USEPYTHON
 TESTSCRIPTS += src/test/test_ntor.sh src/test/test_hs_ntor.sh src/test/test_bt.sh
+
+if COVERAGE_ENABLED
+# ...
+else
+# Only do this when coverage is not on, since it invokes lots of code
+# in a kind of unpredictable way.
 TESTSCRIPTS += src/test/test_rebind.sh
 endif
+endif
 
 TESTS += src/test/test src/test/test-slow src/test/test-memwipe \
 	src/test/test_workqueue \