diff --git a/common/pseudorand.c b/common/pseudorand.c
index 817a9e5bf..c7bff3df6 100644
--- a/common/pseudorand.c
+++ b/common/pseudorand.c
@@ -44,6 +44,13 @@ uint64_t pseudorand_u64(void)
 	return isaac64_next_uint64(&isaac64);
 }
 
+double pseudorand_double(void)
+{
+	init_if_needed();
+
+	return isaac64_next_double(&isaac64);
+}
+
 const struct siphash_seed *siphash_seed(void)
 {
 	init_if_needed();
diff --git a/common/pseudorand.h b/common/pseudorand.h
index 0a46223bf..65272adda 100644
--- a/common/pseudorand.h
+++ b/common/pseudorand.h
@@ -13,6 +13,12 @@ uint64_t pseudorand(uint64_t max);
  */
 uint64_t pseudorand_u64(void);
 
+/**
+ * pseudorand - pseudo (guessable!) random number between 0 (inclusive) and 1
+ * (exclusive).
+ */
+double pseudorand_double(void);
+
 /**
  * Get the siphash seed for hash tables.
  */