diff --git a/inst/tests/tests.Rraw b/inst/tests/tests.Rraw
index a5c0ce3b0..bf63442fb 100644
--- a/inst/tests/tests.Rraw
+++ b/inst/tests/tests.Rraw
@@ -14243,15 +14243,17 @@ test(1997.06, setDTthreads(percent=NULL), error="but is length 0")
 test(1997.07, setDTthreads(percent=1:2), error="but is length 2")
 test(1997.08, setDTthreads(restore_after_fork=21), error="must be TRUE, FALSE, or NULL")
 old = getDTthreads()   # (1)
-oldenv1 = Sys.getenv("R_DATATABLE_NUM_PROCS_PERCENT")
-oldenv2 = Sys.getenv("R_DATATABLE_NUM_THREADS")
+oldenv.PERCENT = Sys.getenv("R_DATATABLE_NUM_PROCS_PERCENT")
+oldenv.THREADS = Sys.getenv("R_DATATABLE_NUM_THREADS")
 Sys.setenv(R_DATATABLE_NUM_THREADS="")  # in case user has this set, so we can test PROCS_PERCENT
-Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT="3.0")
-test(1997.09, setDTthreads(), old, ignore.warning="Ignoring invalid.*Please remove any.*not a digit")
+Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT="3a0")
+test(1997.09, setDTthreads(), old, warning="Ignoring invalid.*")
+Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT="-12.5")
+test(1997.091, setDTthreads(), old, warning="Environment variable.*")
 new = getDTthreads()  # old above at (1) may not have been default. new now is.
 test(1997.10, getDTthreads(), new)
 Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT="1")
-test(1997.11, setDTthreads(), new, ignore.warning="Ignoring invalid.*integer between 2 and 100")
+test(1997.11, setDTthreads(), new, warning="Ignoring invalid.*integer between 2 and 100")
 test(1997.12, getDTthreads(), new)
 Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT="75")
 test(1997.13, setDTthreads(), new)
@@ -14265,14 +14267,26 @@ Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT="75")
 Sys.setenv(R_DATATABLE_NUM_THREADS=allcpu)
 setDTthreads()
 test(1997.15, getDTthreads(), allcpu)
-Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT=oldenv1)
-Sys.setenv(R_DATATABLE_NUM_THREADS=oldenv2)
+Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT=oldenv.PERCENT)
+Sys.setenv(R_DATATABLE_NUM_THREADS=oldenv.THREADS)
 test(1997.16, setDTthreads(old), allcpu)
 test(1997.17, getDTthreads(), old)
 test(1997.18, setDTthreads(throttle=NA), error="throttle.*must be a single number, non-NA, and >=1")
 setDTthreads(throttle=65536)
 test(1997.19, getDTthreads(TRUE), output="throttle==65536")
 setDTthreads(throttle=1024)
+## THRESHOLD test.
+oldenv.PERCENT = Sys.getenv("R_DATATABLE_NUM_PROCS_PERCENT")
+oldenv.THREADS = Sys.getenv("R_DATATABLE_NUM_THREADS")
+oldenv.THRESH = Sys.getenv("_R_CHECK_EXAMPLE_TIMING_CPU_TO_ELAPSED_THRESHOLD_")
+Sys.unsetenv("R_DATATABLE_NUM_THREADS")
+Sys.unsetenv("R_DATATABLE_NUM_PROCS_PERCENT")
+Sys.setenv("_R_CHECK_EXAMPLE_TIMING_CPU_TO_ELAPSED_THRESHOLD_"=2.5)
+setDTthreads()
+test(1997.20, getDTthreads(), 2L)
+Sys.setenv(R_DATATABLE_NUM_PROCS_PERCENT=oldenv.PERCENT)
+Sys.setenv(R_DATATABLE_NUM_THREADS=oldenv.THREADS)
+Sys.setenv("_R_CHECK_EXAMPLE_TIMING_CPU_TO_ELAPSED_THRESHOLD_"=oldenv.THRESH)
 
 # test that a copy is being made and output is printed, #3385 after partial revert of #3281
 x = 5L
diff --git a/src/openmp-utils.c b/src/openmp-utils.c
index 483a91654..e2afb8bfa 100644
--- a/src/openmp-utils.c
+++ b/src/openmp-utils.c
@@ -16,14 +16,18 @@ static int getIntEnv(const char *name, int def)
   size_t nchar = strlen(val);
   if (nchar==0) return def;
   char *end;
-  errno = 0;
-  long int ans = strtol(val, &end, 10);  // ignores leading whitespace. If it fully consumed the string, *end=='\0' and isspace('\0')==false
+  double number = strtod(val, &end);  // ignores leading whitespace. If it fully consumed the string, *end=='\0' and isspace('\0')==false
   while (isspace(*end)) end++;  // ignore trailing whitespace
-  if (errno || (size_t)(end-val)!=nchar || ans<1 || ans>INT_MAX) {
-    warning(_("Ignoring invalid %s==\"%s\". Not an integer >= 1. Please remove any characters that are not a digit [0-9]. See ?data.table::setDTthreads."), name, val);
+  int ans = number;
+  if ((size_t)(end-val)!=nchar) {
+    warning(_("Ignoring invalid %s==\"%s\", which should be interpretable as a number. See ?data.table::setDTthreads."), name, val);
     return def;
   }
-  return (int)ans;
+  if (ans<1 || ans>INT_MAX) {
+    warning(_("Environment variable %s==\"%s\" was interpreted as %d, which is not a positive integer, so instead using default %d. See ?data.table::setDTthreads."), name, val, ans, def);
+    return def;
+  }
+  return ans;
 }
 
 static inline int imin(int a, int b) { return a < b ? a : b; }
@@ -52,6 +56,7 @@ void initDTthreads(void) {
   // max_threads() -vs- num_procs(): https://software.intel.com/en-us/forums/intel-visual-fortran-compiler-for-windows/topic/302866
   ans = imin(ans, getIntEnv("OMP_THREAD_LIMIT", INT_MAX));  // user might expect `Sys.setenv(OMP_THREAD_LIMIT=2);setDTthreads()` to work. Satisfy this
   ans = imin(ans, getIntEnv("OMP_NUM_THREADS", INT_MAX));   //   expectation by reading them again now. OpenMP just reads them on startup (quite reasonably)
+  ans = imin(ans, getIntEnv("_R_CHECK_EXAMPLE_TIMING_CPU_TO_ELAPSED_THRESHOLD_", INT_MAX));// CRAN sets this to 2.5 during checks.
   ans = imax(ans, 1);  // just in case omp_get_* returned <=0 for any reason, or the env variables above are set <=0
   DTthreads = ans;
   DTthrottle = imax(1, getIntEnv("R_DATATABLE_THROTTLE", 1024)); // 2nd thread is used only when n>1024, 3rd thread when n>2048, etc