diff --git a/src/poetry/core/packages/constraints/__init__.py b/src/poetry/core/packages/constraints/__init__.py
index d61a2cb79..33cc902e4 100644
--- a/src/poetry/core/packages/constraints/__init__.py
+++ b/src/poetry/core/packages/constraints/__init__.py
@@ -51,12 +51,14 @@ def parse_single_constraint(constraint: str) -> Constraint:
     m = BASIC_CONSTRAINT.match(constraint)
     if m:
         op = m.group(1)
+
         if op is None:
             op = "=="
+            version = constraint
+        else:
+            version = f"{constraint.strip()[len(op.strip()):]}"
 
-        version = m.group(2).strip()
-
-        return Constraint(version, op)
+        return Constraint(version.strip(), op)
 
     raise ValueError(f"Could not parse version constraint: {constraint}")
 
diff --git a/src/poetry/core/semver/helpers.py b/src/poetry/core/semver/helpers.py
index 9022add94..40c17dcf6 100644
--- a/src/poetry/core/semver/helpers.py
+++ b/src/poetry/core/semver/helpers.py
@@ -125,14 +125,18 @@ def parse_single_constraint(constraint: str) -> VersionConstraint:
     m = BASIC_CONSTRAINT.match(constraint)
     if m:
         op = m.group(1)
-        version_string = m.group(2)
-
-        # Technically invalid constraints like `>= 3.*` will appear
-        # here as `3.`.
-        # Pip currently supports these and to avoid breaking existing
-        # users workflows we need to support them as well. To do so,
-        # we just remove the inconsequential part.
-        version_string = version_string.rstrip(".")
+        version_string = (
+            f"{constraint.strip()[len(op.strip()):]}" if op else constraint.strip()
+        )
+
+        if version_string.endswith(".*"):
+            # Technically invalid constraints like `>= 3.*` will appear
+            # here as `3.*`.
+            #
+            # Pip currently supports these and to avoid breaking existing
+            # users workflows we need to support them as well. To do so,
+            # we just remove the inconsequential part.
+            version_string = version_string[:-2]
 
         if version_string == "dev":
             version_string = "0.0-dev"
diff --git a/tests/semver/test_parse_constraint.py b/tests/semver/test_parse_constraint.py
index 5e80626af..e6d776a20 100644
--- a/tests/semver/test_parse_constraint.py
+++ b/tests/semver/test_parse_constraint.py
@@ -182,6 +182,28 @@
                 include_min=True,
             ),
         ),
+        (
+            "^1.0.0a1.dev0",
+            VersionRange(
+                min=Version.from_parts(
+                    1, 0, 0, pre=ReleaseTag("a", 1), dev=ReleaseTag("dev", 0)
+                ),
+                max=Version.from_parts(2, 0, 0),
+                include_min=True,
+            ),
+        ),
+        (
+            "1.0.0a1.dev0",
+            VersionRange(
+                min=Version.from_parts(
+                    1, 0, 0, pre=ReleaseTag("a", 1), dev=ReleaseTag("dev", 0)
+                ),
+                max=Version.from_parts(
+                    1, 0, 0, pre=ReleaseTag("a", 1), dev=ReleaseTag("dev", 0)
+                ),
+                include_min=True,
+            ),
+        ),
         (
             "~1.0.0a1",
             VersionRange(
@@ -190,6 +212,16 @@
                 include_min=True,
             ),
         ),
+        (
+            "~1.0.0a1.dev0",
+            VersionRange(
+                min=Version.from_parts(
+                    1, 0, 0, pre=ReleaseTag("a", 1), dev=ReleaseTag("dev", 0)
+                ),
+                max=Version.from_parts(1, 1, 0),
+                include_min=True,
+            ),
+        ),
         (
             "^0",
             VersionRange(
diff --git a/tests/version/test_requirements.py b/tests/version/test_requirements.py
index 556ed842d..1073aeb9c 100644
--- a/tests/version/test_requirements.py
+++ b/tests/version/test_requirements.py
@@ -47,6 +47,7 @@ def assert_requirement(
         ("name<3.*", {"name": "name", "constraint": "<3.0"}),
         ("name>3.5.*", {"name": "name", "constraint": ">3.5"}),
         ("name==1.0.post1", {"name": "name", "constraint": "==1.0.post1"}),
+        ("name==1.2.0b1.dev0", {"name": "name", "constraint": "==1.2.0b1.dev0"}),
         (
             "name>=1.2.3;python_version=='2.6'",
             {