diff --git a/include/optparse.h b/include/optparse.h
index ecc0036a..7a6f815c 100644
--- a/include/optparse.h
+++ b/include/optparse.h
@@ -53,7 +53,8 @@ char *hostport_param(char *param, char **host, char **port);
 uint32_t atouint32_metric(const char *str, const char *error_hint);
 
 /// Convert a string to an integer, uses strtod() and accepts
-/// time suffixes of 's', 'm', and 'h' (also 'S', 'M', and 'H').
+/// time suffixes of 'd', 'h', 'm', and 's' (also 'D', 'H', 'M', and 'S'),
+/// or the form hours:minutes[:seconds].
 ///
 /// Parse errors will fprintf(stderr, ...) and exit(1).
 ///
diff --git a/src/optparse.c b/src/optparse.c
index 3eb5e1f7..5e5d12bb 100644
--- a/src/optparse.c
+++ b/src/optparse.c
@@ -156,35 +156,69 @@ int atoi_time(const char *str, const char *error_hint)
         exit(1);
     }
 
-    char *endptr;
-    double val = strtod(str, &endptr);
+    char *endptr    = (char *)str;
+    double val      = 0.0;
+    unsigned colons = 0;
 
-    if (str == endptr) {
-        fprintf(stderr, "%sinvalid time argument (%s)\n", error_hint, str);
-        exit(1);
-    }
+    while (*endptr) {
+        double num = strtod(str, &endptr);
 
-    // allow whitespace before suffix
-    while (*endptr == ' ' || *endptr == '\t')
-        ++endptr;
+        if (str == endptr) {
+            fprintf(stderr, "%sinvalid time argument (%s)\n", error_hint, str);
+            exit(1);
+        }
 
-    switch (*endptr) {
+        // allow whitespace before suffix
+        while (*endptr == ' ' || *endptr == '\t')
+            ++endptr;
+
+        switch (*endptr) {
         case '\0':
+            if (colons == 0) {
+                // assume seconds
+                val += num;
+                break;
+            }
+        case ':':
+            ++colons;
+            if (colons == 1)
+                val += num * 60 * 60;
+            else if (colons == 2)
+                val += num * 60;
+            else if (colons == 3)
+                val += num;
+            else {
+                fprintf(stderr, "%stoo many colons (use HH:MM[:SS]))\n", error_hint);
+                exit(1);
+            }
+            if (*endptr)
+                ++endptr;
             break;
         case 's':
         case 'S':
+            val += num;
+            ++endptr;
             break;
         case 'm':
         case 'M':
-            val *= 60;
+            val += num * 60;
+            ++endptr;
             break;
         case 'h':
         case 'H':
-            val *= 60 * 60;
+            val += num * 60 * 60;
+            ++endptr;
+            break;
+        case 'd':
+        case 'D':
+            val += num * 60 * 60 * 24;
+            ++endptr;
             break;
         default:
             fprintf(stderr, "%sunknown time suffix (%s)\n", error_hint, endptr);
             exit(1);
+        }
+        str = endptr;
     }
 
     if (val > INT_MAX || val < INT_MIN) {