Update per Sebastian's comments

3 files changed, 14 insertions, 7 deletions

diff --git a/numpy/core/_add_newdocs.py b/numpy/core/_add_newdocs.py
index 30379dfbe..8580904e2 100644
--- a/numpy/core/_add_newdocs.py
+++ b/numpy/core/_add_newdocs.py
@@ -1036,10 +1036,8 @@ add_newdoc('numpy.core.multiarray', 'fromstring',
         A string containing the data.
     dtype : data-type, optional
         The data type of the array; default: float.  For binary input data,
-        the data must be in exactly this format.  Supported dtypes are
-        byte, ubyte, short, ushort, int, uint, long, ulong, longlong, ulonglong,
-        datetime, timedelta, float, double, longdouble, half, bool, 
-        cfloat, and cdouble.
+        the data must be in exactly this format. Most builtin numeric types are 
+        supported and extension types may be supported.
 
         Complex dtypes are only supported since numpy 1.18.0
     count : int, optional
diff --git a/numpy/core/src/multiarray/arraytypes.c.src b/numpy/core/src/multiarray/arraytypes.c.src
index c06a1edaa..9ffa30d81 100644
--- a/numpy/core/src/multiarray/arraytypes.c.src
+++ b/numpy/core/src/multiarray/arraytypes.c.src
@@ -1873,15 +1873,18 @@ static int
         result = NumPyOS_ascii_strtod(str, endptr);
 
         if (endptr && *endptr[0] == 'j') {
+            // Read is successful if the immediate following char is j
             output.imag = result;
+
+            // Skip j
+            ++*endptr;
         }
         else {
+            // Set endptr to previous char to trigger the not everything is
+            // read error
             endptr = prev;
             output.imag = 0;
         }
-
-        // Skip j
-        ++*endptr;
     }
     else if (endptr && *endptr[0] == 'j') {
         // Real component not specified
diff --git a/numpy/core/tests/test_longdouble.py b/numpy/core/tests/test_longdouble.py
index b9652cc98..74dcb4d5e 100644
--- a/numpy/core/tests/test_longdouble.py
+++ b/numpy/core/tests/test_longdouble.py
@@ -95,6 +95,12 @@ def test_fromstring_complex():
         with assert_warns(DeprecationWarning):
             assert_equal(np.fromstring("1+j", dtype=ctype, sep=","),
                          np.array([1.]))
+        with assert_warns(DeprecationWarning):
+            assert_equal(np.fromstring("1+", dtype=ctype, sep=","),
+                         np.array([1.]))
+        with assert_warns(DeprecationWarning):
+            assert_equal(np.fromstring("1j+1", dtype=ctype, sep=","),
+                         np.array([1j]))