diff --git a/source/blender/blenkernel/intern/unit.cc b/source/blender/blenkernel/intern/unit.cc
index a89806b3801..9c4db7c77da 100644
--- a/source/blender/blenkernel/intern/unit.cc
+++ b/source/blender/blenkernel/intern/unit.cc
@@ -1844,6 +1844,18 @@ static bool ch_is_op(char op)
   }
 }
 
+static bool ch_is_op_unary(char op)
+{
+  switch (op) {
+    case '+':
+    case '-':
+    case '~':
+      return true;
+    default:
+      return false;
+  }
+}
+
 /**
  * Helper function for #unit_distribute_negatives to find the next negative to distribute.
  *
@@ -1912,6 +1924,18 @@ static char *find_next_op(const char *str, char *remaining_str, int remaining_st
   return remaining_str + i;
 }
 
+/**
+ * Skip over multiple successive unary operators (typically `-`), skipping spaces.
+ * This allows for `--90d` to be handled properly, see: #117783.
+ */
+static char *skip_unary_op(char *str)
+{
+  while (*str == ' ' || ch_is_op_unary(*str)) {
+    str++;
+  }
+  return str;
+}
+
 /**
  * Put parentheses around blocks of values after negative signs to get rid of an implied "+"
  * between numbers without an operation between them. For example:
@@ -1937,8 +1961,9 @@ static bool unit_distribute_negatives(char *str, const int str_maxncpy)
     memmove(remaining_str + 1, remaining_str, remaining_str_maxncpy - 2);
     *remaining_str = '(';
 
-    /* Add the ')' before the next operation or at the end. */
-    remaining_str = find_next_op(str, remaining_str + 1, remaining_str_maxncpy);
+    /* Add the ')' before the next operation or at the end.
+     * Unary operators are skipped to allow `--` to be a supported prefix. */
+    remaining_str = find_next_op(str, skip_unary_op(remaining_str + 1), remaining_str_maxncpy);
     remaining_str_maxncpy = str_maxncpy - int(remaining_str - str);
     memmove(remaining_str + 1, remaining_str, remaining_str_maxncpy - 2);
     *remaining_str = ')';
diff --git a/tests/python/bl_pyapi_bpy_utils_units.py b/tests/python/bl_pyapi_bpy_utils_units.py
index e80aa833ec6..ab86b22fab9 100644
--- a/tests/python/bl_pyapi_bpy_utils_units.py
+++ b/tests/python/bl_pyapi_bpy_utils_units.py
@@ -29,6 +29,24 @@ class UnitsTesting(unittest.TestCase):
         ('METRIC', 'LENGTH', "", "1+1ft", 1.3048),  # no metric units, we default to meters.
         ('IMPERIAL', 'LENGTH', "", "3+1in+1ft", 0.3048 * 4 + 0.0254),  # bigger unit becomes default one!
         ('IMPERIAL', 'LENGTH', "", "(3+1)in+1ft", 0.3048 + 0.0254 * 4),
+
+        # Support successive leading unary operators.
+        ('IMPERIAL', 'LENGTH', "", "-1ft", -0.3048),
+        ('IMPERIAL', 'LENGTH', "", "--1ft", --0.3048),
+        ('IMPERIAL', 'LENGTH', "", "---1ft", ---0.3048),
+
+        ('IMPERIAL', 'LENGTH', "", "- 1ft", -0.3048),
+        ('IMPERIAL', 'LENGTH', "", "- - 1ft", --0.3048),
+        ('IMPERIAL', 'LENGTH', "", "- - - 1ft", ---0.3048),
+
+        ('IMPERIAL', 'LENGTH', "", "-+1ft", -+0.3048),
+        ('IMPERIAL', 'LENGTH', "", "+-1ft", +-0.3048),
+
+        ('METRIC', 'LENGTH', "", "~+-32m", ~+-32),
+        ('METRIC', 'LENGTH', "", "-+~32m", -+~32),
+
+        ('METRIC', 'LENGTH', "", "~ + - 32m", ~+-32),
+        ('METRIC', 'LENGTH', "", "- + ~ 32m", -+~32),
     )
 
     # From 'internal' Blender value to user-friendly printing