diff --git a/py/objcomplex.c b/py/objcomplex.c
index 65957cbf60..2ba5226150 100644
--- a/py/objcomplex.c
+++ b/py/objcomplex.c
@@ -6,6 +6,7 @@
 #include "mpconfig.h"
 #include "qstr.h"
 #include "obj.h"
+#include "parsenum.h"
 #include "runtime0.h"
 #include "map.h"
 
@@ -36,15 +37,20 @@ STATIC mp_obj_t complex_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const
             return mp_obj_new_complex(0, 0);
 
         case 1:
-            // TODO allow string as first arg and parse it
-            if (MP_OBJ_IS_TYPE(args[0], &mp_type_complex)) {
+            if (MP_OBJ_IS_STR(args[0])) {
+                // a string, parse it
+                uint l;
+                const char *s = mp_obj_str_get_data(args[0], &l);
+                return mp_parse_num_decimal(s, l, true, true);
+            } else if (MP_OBJ_IS_TYPE(args[0], &mp_type_complex)) {
+                // a complex, just return it
                 return args[0];
             } else {
+                // something else, try to cast it to a complex
                 return mp_obj_new_complex(mp_obj_get_float(args[0]), 0);
             }
 
-        case 2:
-        {
+        case 2: {
             mp_float_t real, imag;
             if (MP_OBJ_IS_TYPE(args[0], &mp_type_complex)) {
                 mp_obj_complex_get(args[0], &real, &imag);
diff --git a/py/objfloat.c b/py/objfloat.c
index 65dafa607e..c51e13e7a1 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -38,10 +38,12 @@ STATIC mp_obj_t float_make_new(mp_obj_t type_in, uint n_args, uint n_kw, const m
                 // a string, parse it
                 uint l;
                 const char *s = mp_obj_str_get_data(args[0], &l);
-                return mp_parse_num_decimal(s, l, false);
+                return mp_parse_num_decimal(s, l, false, false);
             } else if (MP_OBJ_IS_TYPE(args[0], &mp_type_float)) {
+                // a float, just return it
                 return args[0];
             } else {
+                // something else, try to cast it to a float
                 return mp_obj_new_float(mp_obj_get_float(args[0]));
             }
 
diff --git a/py/parsenum.c b/py/parsenum.c
index b1a70c352d..77f00957c6 100644
--- a/py/parsenum.c
+++ b/py/parsenum.c
@@ -88,7 +88,7 @@ mp_obj_t mp_parse_num_integer(const char *restrict str, uint len, int base) {
 #define PARSE_DEC_IN_FRAC (2)
 #define PARSE_DEC_IN_EXP  (3)
 
-mp_obj_t mp_parse_num_decimal(const char *str, uint len, bool allow_imag) {
+mp_obj_t mp_parse_num_decimal(const char *str, uint len, bool allow_imag, bool force_complex) {
 #if MICROPY_ENABLE_FLOAT
     const char *top = str + len;
     mp_float_t dec_val = 0;
@@ -129,7 +129,7 @@ mp_obj_t mp_parse_num_decimal(const char *str, uint len, bool allow_imag) {
             dec_val = MICROPY_FLOAT_C_FUN(nan)("");
         }
     } else {
-        // parse the digits
+        // string should be a decimal number
         int in = PARSE_DEC_IN_INTG;
         bool exp_neg = false;
         int exp_val = 0;
@@ -198,6 +198,8 @@ mp_obj_t mp_parse_num_decimal(const char *str, uint len, bool allow_imag) {
     // return the object
     if (imag) {
         return mp_obj_new_complex(0, dec_val);
+    } else if (force_complex) {
+        return mp_obj_new_complex(dec_val, 0);
     } else {
         return mp_obj_new_float(dec_val);
     }
diff --git a/py/parsenum.h b/py/parsenum.h
index f87fefbe77..97578423c7 100644
--- a/py/parsenum.h
+++ b/py/parsenum.h
@@ -1,2 +1,2 @@
 mp_obj_t mp_parse_num_integer(const char *restrict str, uint len, int base);
-mp_obj_t mp_parse_num_decimal(const char *str, uint len, bool allow_imag);
+mp_obj_t mp_parse_num_decimal(const char *str, uint len, bool allow_imag, bool force_complex);
diff --git a/py/runtime.c b/py/runtime.c
index 5604e1a945..c268fd5464 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -375,7 +375,7 @@ mp_obj_t rt_load_const_dec(qstr qstr) {
     DEBUG_OP_printf("load '%s'\n", qstr_str(qstr));
     uint len;
     const byte* data = qstr_data(qstr, &len);
-    return mp_parse_num_decimal((const char*)data, len, true);
+    return mp_parse_num_decimal((const char*)data, len, true, false);
 }
 
 mp_obj_t rt_load_const_str(qstr qstr) {